PHYSICS FORM4 REVISION QUESTION

FORM 4 NOTES Name: ______________________ Class: ___________ Teacher: Mr.Henry Rushema Theme 3 -The Nature of Waves 1 • Waves carry _______________ from one place to another. • There are two kinds of waves: a) Transverse waves b) Longitudinal waves. Transverse waves Transverse waves are made up of _________________ and ____________________. Definition of a transverse wave: It is a wave in which the vibrations are _________________________ (900 ) to the direction of the wave. Examples of transverse waves: ____________________, _________________, __________________. Longitudinal waves Longitudinal waves are made up of ______________________ and ________________________. Definition of a longitudinal wave: It is a wave in which the vibrations are ________________________ (1800 ) to the direction of the wave. Example of longitudinal wave: ______________________. http://www.youtube.com/watch_popup?v=Rbuhdo0AZDU 2 Wavelength ( λ ) S.I. unit: metre (m) The wavelength of a wave is the length of a single wave. It is denoted by the Greek letter λ (read as lambda). a) Transverse waves The wavelength ( λ ) for a transverse wave is the length of a single wave made up of a crest and a trough. However, it is also equal to the distance between two successive ______________ or two successive ___________________. b) Longitudinal waves The wavelength ( λ ) for a longitudinal wave is the length of a single wave made up of a compression and a rarefaction. However, it is also equal to the distance between two successive ______________________ or two successive ___________________. http://einstein.byu.edu/~masong/HTMstuff/WaveTrans.html Amplitude and Displacement S.I. unit: metre (m) The displacement is the height of the wave, from its rest position. The maximum displacement is called __________________. So the amplitude is the height of a crest or the depth of a trough. The greater the amplitude, the greater the ________________ of the wave. At which points is the displacement zero metres? _____________________________________ At which points do we measure the amplitude? _____________________________________ 3 dimensional view 3 Waves, cycles and oscillations 1 wave = 1 cycle = 1 oscillation Frequency (f) S.I. unit: Hertz (Hz) Definition: It is the number of waves in _________ second. If 5 waves are generated in one second, then the frequency = ___________. If 100 waves are generated in one second, then the frequency = __________. The frequency of a wave can only change if the frequency of the source changes. If you dip your finger in water 3 times in 1 second, your frequency (the source) is 3Hz and the frequency of the waves is also 3Hz as 3 waves are produced every second. If the waves move in deep or shallow water the frequency will still be 3Hz as you would still be producing 3 waves in one second. Unless you change your frequency (source), the frequency of the waves will not change. Periodic Time (T) S.I. unit: seconds (s) Definition: It is the time taken to complete one wave. If it takes 3 seconds to complete one wave, then the periodic time = ___________. If it takes 0.2 seconds to complete one wave, then the periodic time = __________. f = 1 and T = 1 T f Example: If 5 waves are produced in one second, find: a) the frequency, b) the periodic time. _______________________________________________________________________________________ _______________________________________________________________________________________ Mr. N.Briffa HOD Theme 3 -The Nature of Waves Mr. N. Briffa B.Ed (Hons.) 4 Frequency (f) = no of waves in 1 second Periodic Time (T) = Time for one complete wave Ex 1 Ex 2 Ex 3 Ex 4 Ex 5 Ex 6 Ex 7 Find the: a) Periodic time _________________________________ b) Frequency __________________________________ Ex 8 Six waves hit a breakwater every minute. Find the: a) frequency ____________________________________________________________________ b) periodic time ____________________________________________________________________ 5 Ex 9 The pendulum takes 2 seconds to swing from A to B. If the horizontal distance from A to B is 1m, find: a) its amplitude of vibration _______________________________ b) its periodic time _______________________________________ c) its frequency __________________________________________ Ex 10 During an earthquake, the upper part of a skyscraper moves from side to side, a horizontal distance of 4m in 1.2 seconds. Find: a) its amplitude of vibration _______________________________ b) its periodic time _______________________________________ c) its frequency __________________________________________ Ex 11 The ruler is placed at the edge of a table and is set to vibrate as shown. If the end of the ruler moves a vertical distance of 3cm in 0.2 seconds, find: a) its amplitude of vibration _______________________________ b) its periodic time _______________________________________ c) its frequency __________________________________________ Wave Velocity (v or c) S.I. unit: metres per second (m/s) This is the velocity with which the wave travels. Velocity = Frequency x Wavelength v = f λ (m/s) (Hz) (m) Example 1: Find the velocity of a wave having a frequency of 3Hz and a wavelength of 0.4m. _______________________________________________________________________________________ _______________________________________________________________________________________ Example 2: Find the frequency of a wave which is moving at 2m/s and which has a wavelength of 30cm. _______________________________________________________________________________________ _______________________________________________________________________________________ 6 The Electromagnetic Spectrum • Gamma rays have the ____________________ frequency, the _____________________ energy and the __________________________ wavelength. • Radio waves have the _____________________ frequency, the _______________________ energy and the __________________________ wavelength. Gamma rays, X-rays, Ultraviolet, Visible light, Infra-red, Microwaves and Radio waves are all electromagnetic waves that make up the _____________________________________________. Except for visible light, all the other waves are invisible to the human eye. Common properties of Electromagnetic waves: 1. They are all __________________________ waves. 2. They do not need a medium to travel through, so they can travel in a ________________________. 3. They have a common ___________________ (3 x 108 m/s or 300,000,000 m/s). 4. Being waves they all carry __________________. 5. They obey the laws of reflection, refraction and diffraction. 6. They are uncharged. (not + or - ) Mr. N.Briffa HOD Theme 3 -The Nature of Waves Mr. N. Briffa B.Ed (Hons.) 7 Approximate λ (m) Source Use Additional information Gamma Is very penetrating and can be very dangerous if used inappropriately. Can be detected with a Geiger-Muller tube. X-rays Produced when electrons hit a metal target. Can penetrate flesh but not bones and so produces a shadow, making fractures visible. Parts of the body need to be covered with lead. Can be detected by photographic plates. Ultraviolet Can be detected by using fluorescent chemicals making objects glow in the dark. Visible light The only radiation which we can see. Can be further divided into seven colours. Infra-red They can be detected by using a thermometer with a blackened bulb. Microwaves Microwaves make the water particles contained in food vibrate causing heating. They cause burns if absorbed by the body. Radio waves Information is encoded into a radio wave, transmitted to a receiver where it is decoded. Mr. N.Briffa HOD Theme 3 -The Nature of Waves Mr. N. Briffa B.Ed (Hons.) 8 Ripple tank Water waves are transverse waves. They can be studied in a __________________________. Architects and engineers use ripple tanks to study the best design for breakwaters before they start projects on a large scale. How do you produce straight waves in a ripple tank? By using a _____________________ that is forced to move up and down by an electric motor. How do you produce circular waves in a ripple tank? By using a _____________________ that is forced to move up and down by an electric motor. A _____________________ is an instrument that makes waves appear stationary. The ___________________ is equal to the distance between two successive wavefronts and is measured with a metre ruler. Reflection of water waves The angle of incidence (i) is equal to the angle of reflection (r). Draw the normal and the reflected wavefronts in each diagram. Underline the correct answer: After the waves are reflected: a) the wavelength ( increases, remains the same, decreases) b) the frequency ( increases, remains the same, decreases) c) the velocity ( increases, remains the same, decreases) Mr. N.Briffa HOD Theme 3 -The Nature of Waves Mr. N. Briffa B.Ed (Hons.) 9 Refraction of water waves When water waves change the depth, they change direction because they change their _____________. Underline the correct answer: When the wavefronts pass from deep water to shallow water: • the wavelength (increases, remains the same, decreases) • the frequency (increases, remains the same, decreases) • the velocity (increases, remains the same, decreases) • the wave changes direction and is refracted (towards, away from) the normal. Underline the correct answer: When the wavefronts pass from shallow water to deep water: • the wavelength (increases, remains the same, decreases) • the frequency (increases, remains the same, decreases) • the velocity (increases, remains the same, decreases) • the wave changes direction and is refracted (towards, away from) the normal. http://www.youtube.com/watch_popup?v=r0088hYFuws Mr. N.Briffa HOD Theme 3 -The Nature of Waves Mr. N. Briffa B.Ed (Hons.) 10 Complete the diagrams below. http://www.youtube.com/watch_popup?v=stdi6XJX6gU If the wavefronts enter the shallow water along the normal, they are not refracted. However the wavelength and the speed still _______________ in shallow water and _________________ in deep water. The frequency does not change. Mr. N.Briffa HOD Theme 3 -The Nature of Waves Mr. N. Briffa B.Ed (Hons.) 11 Question: A graph of the displacement against distance for a wave is shown in the diagram. a) Using the graph, find the amplitude of the wave. ____________________________________________________________________________(1 mark) b) Using the graph, find the wavelength of the wave. ____________________________________________________________________________ (1 mark) c) If the frequency of the source is 100Hz, calculate the velocity of the wave. ____________________________________________________________________________(2 marks) d) The wave enters a medium and slows down. What change, if any, is there in the frequency? ____________________________________________________________________________(2 marks) e) What change if any is there in the wavelength? ____________________________________________________________________________(2 marks) f) How would the same graph be different if the wave had more energy? ____________________________________________________________________________(2 marks) Mr. N.Briffa HOD Theme 3 -The Nature of Waves Mr. N. Briffa B.Ed (Hons.) 12 Diffraction of water waves When water waves pass through a gap they spread or __________________. The diffraction is greatest when the gap width is similar to the wavelength of the wave. Spreading of waves is not desired in harbours. The narrow gap being similar to the wavelength of the waves causes more diffraction (spreading) of waves and this would not be ideal for a harbour. http://www.ngsir.netfirms.com/englishhtm/Diffraction.htm http://www.youtube.com/watch_popup?v=4EDr2YY9lyA 13 Question: Harbours have breakwaters to stop large waves. a i) What is the wavelength of the water waves? __________________________________________________________________________(2 marks) ii) 5 waves hit the breakwater every 20 seconds. What is the frequency of the water waves? ________________________________________________________________________________ __________________________________________________________________________ (2 marks) iii) Calculate the velocity of the waves. __________________________________________________________________________ (2 marks) b i) Complete the diagram above to show how the waves proceed after passing through the gap. (2 marks) ii) Explain why it would not be wise to make the gap too narrow. ________________________________________________________________________________ __________________________________________________________________________ (2 marks) 14 Question: This question is about an experimental design about water waves. a) A tank 5 m long is filled with water. Using the apparatus above, describe how one could find the speed of the water wave. ___________________________________________________________________________________ ___________________________________________________________________________________ ___________________________________________________________________________________ ___________________________________________________________________________(4 marks) b) A student is told that the deeper the water, the less the wave velocity. Describe how he should investigate this statement. Method: ___________________________________________________________________________________ ___________________________________________________________________________________ ___________________________________________________________________________________ ___________________________________________________________________________(3 marks) Table of results: (2 marks) Graph: ___________________________________________________________________________ (1 mark) Precautions: ___________________________________________________________________________________ ___________________________________________________________________________________ ___________________________________________________________________________ (3 marks) From the shape of the graph, how could the student tell if the statement is correct? ___________________________________________________________________________________ ___________________________________________________________________________(2 marks) measuring tape stopwatch Mr. N.Briffa HOD Theme 3 -The Nature of Waves Mr. N. Briffa B.Ed (Hons.) 15 SOUND Sound energy travels in the form of longitudinal waves. A longitudinal wave is made up of _______________________ (C) and ____________________ (R). How does sound travel through air? By means of compressions and rarefactions of air particles. Sound waves from a loudspeaker produce compressions and rarefactions of invisible air molecules. A compression is a region in which the number of air molecules (particles) is high. A rarefaction is a region in which the number of air molecules is low. The speaker has a cone which is made to vibrate in and out by an electric current. When the cone moves, out the air in front is compressed and when it moves in, the air is rarefied. Sound is not electromagnetic in nature as it requires a medium to travel. Sound does not travel in a vacuum. If an explosion occurs in space, nothing will be heard as there the sound cannot travel. Experiment: To show that sound requires a medium to travel. As air is pumped out by a vacuum pump, the ringing of the bell gets lower and lower. When all the air is removed, the hammer can be seen vibrating but no sound is heard. This experiment shows that sound does not travel in a __________________. Mr. N.Briffa HOD Theme 3 -The Nature of Waves Mr. N. Briffa B.Ed (Hons.) 16 The tuning fork This is an instrument which after being struck vibrates at a certain frequency. If it has a frequency of 256Hz, it means that it vibrates 256 times in one second. Characteristics of sound a) Pitch: Pitch is a term used by musicians to distinguish different notes. The higher the pitch, the higher the _____________________. b) Loudness: The loudness of a sound wave depends on how much ______________ it has. The loudness and energy depend on the ____________________ of the sound wave. Another word for loudness is _________________. Both sounds have the same pitch as the tuning forks vibrate at the same frequency. So pitch and loudness are independent of each other. c) Quality (timbre): The same note on different instruments sounds differently even though they have same pitch and loudness. A tuning fork of frequency 256 Hz produces a sound with a high pitch (diiing). A tuning fork of frequency 128 Hz produces a sound with a low pitch (dooong). A tuning fork of frequency 256 Hz struck hard produces a loud sound with large amplitude. The tuning fork of frequency 256 Hz struck gently produces a quiet sound with a small amplitude. 17 Question: In the lab a student connects a microphone to an oscilloscope so that it can be used to detect sound waves. A loudspeaker producing a note of frequency 300Hz is placed in line with the microphone. The trace obtained on the oscilloscope screen is shown in Figure 1. Figure 1 Figure 2 Figure 3 a) Explain how a sound wave travels through the air, from the loudspeaker to the microphone. _____________________________________________________________________________________ _____________________________________________________________________________ (2 marks) b) If the velocity of sound in air is 330 m/s, what is the wavelength of the sound emitted? _____________________________________________________________________________ (2 marks) c) The student decreases the intensity (loudness) of the sound produced but does not change the frequency. Draw the new trace produced on the screen in Figure 2. (2 marks) d) The sound intensity is changed back to its initial value and this time the frequency is varied from 300Hz to 600Hz. Draw the trace of the new note of frequency 600 Hz in Figure 3. (2 marks) e) The loudspeaker and microphone are now placed inside a sealed jar, as shown below. The loudspeaker produces a note of 300 Hz, and with the jar full of air the trace produced is as shown in Figure 1. If all the air is pumped out of the jar, what trace is now seen on the oscilloscope? Explain. _____________________________________________________________________________________ ____________________________________________________________________________ (2 marks) (Total 10 marks) 18 Question: The following are traces seen on an oscilloscope when 4 different sounds are produced. A B C D Which of the figures represents: Speed of sound ANY sound in air travels at around 330 m/s. It does not depend on pitch or loudness. The speed of sound is affected by the temperature and the material through which it travels. The higher the temperature, the _______________ the sound travels. Material Speed of sound (m/s) Air Water Steel Reflection of sound Sound waves are reflected when incident onto a surface. The reflected sound is called an ___________. An echo is less loud than the original sound. This is because it has less energy. Example : A man standing at a distance of 200 m from a large high wall, produces a sound and hears an echo after 1.2 seconds. Find the speed of sound in air. _______________________________________________________________________________________ _______________________________________________________________________________________ A loud high pitch sound. A quiet high pitch sound. A loud low pitch sound. A quiet low pitch sound. Mr. N.Briffa HOD Theme 3 -The Nature of Waves Mr. N. Briffa B.Ed (Hons.) 19 Measuring the speed of sound Method 1: A sound is produced (e.g. by clapping once). When the sound reaches microphone X, _____________________________________. When the sound reaches microphone Y, _____________________________________. The distance d is measured with a metre rule and the formula Speed = Distance is used. Time Method 2: A person standing at a distance of about 100 m from a large high wall, claps his hands at regular intervals to coincide exactly with the echoes. The time taken for 50 claps is recorded. The distance for each echo heard is 2 x 100 m = 200 m The time for one echo is found by measuring the total time for 50 echoes and finding an average. ( ex. if the total time is 30 seconds, average time = 30 ÷ 50 = 0.6 seconds) Using the formula: Average speed = Distance = 200 m … will give the speed of sound in air. Time time for one echo Mr. N.Briffa HOD Theme 3 -The Nature of Waves Mr. N. Briffa B.Ed (Hons.) 20 Example : An echo sounder in a trawler receives an echo from the sea bed 2 seconds after it is sent. If the speed of sound in water is 1500m/s, how deep is the sea? _____________________________________________________________________ __________________ Question: Luke and David are standing between 2 walls A and B, 480 m from the nearest wall. David beats his drum and Luke hears the first echo after 3 seconds. a) Explain why Luke hears an echo. __________________________________________________________________________(2 marks) b) Calculate the velocity of sound in air. __________________________________________________________________________(2 marks) c) If a second echo is heard 2 seconds later, what is the distance between the walls? ____________________________________________________________________________________ _______________________________________________________________________________________ _____________________________________________________________________________(3 marks) d) Luke tries to measure the speed of sound in a liquid. The equipment used is shown below. Explain briefly how the speed is measured. ___________________________________________ ___________________________________________ ___________________________________________ ___________________________________________ ___________________________________________ ___________________________________(3 marks) Ultrasound We can hear sounds with a frequency between ______ Hz and _________Hz. Sound waves with a frequency higher than 20,000Hz (20kHz) are called _____________________. Therefore ultrasound waves are just _______________ waves with a very high frequency. A dog’s whistle produces ultrasonic sounds. • Ships use an echo sounding system called sonar, which uses ultrasound to measure the _________________________________________ and to detect ______________________________. • Doctors use ultrasound to scan ________________________ in the body and monitor unborn babies. • Bats and dolphins use ultrasound to know how far they are from objects and to hunt (echolocation). • Detect flaws in welding. Mr. N.Briffa HOD Theme 3 -The Nature of Waves Mr. N. Briffa B.Ed (Hons.) 21 This is a question about the use of ultrasound by bats. The first known work with ultrasound was carried out by Lazzaro Spallanzani, an Italian scientist who wondered how bats can fly in complete darkness. He blindfolded them and noticed that they still could fly well. He then plugged their ears and found that they bumped into obstacles. He concluded that they must emit sound waves which we cannot hear and then listen to the echoes to determine the distance and direction of objects. a) What is the normal range of hearing for human beings? ________________________________________________________________________ [1] b) How does sound travel through air? ________________________________________________________________________ [1] c) Is ultrasound made up of transverse or longitudinal waves? ________________________________________________________________________ [1] d) A bat emits a sound with a frequency of 34 kHz. (i) What is meant by the term frequency? ________________________________________________________________________ [1] (ii) What is the value of the above frequency in Hertz? ________________________________________________________________________ [1] (iii) Calculate the wavelength of the sound waves produced, if their speed in air is 340 m/s. ________________________________________________________________________ [1] e) The bat is flying close to a wall and receives the reflected sound after 0.16 s. (i) What is the reflected sound called? ________________________________________________________________________ [1] (ii) Calculate the distance between the bat and the wall. ________________________________________________________________________ [1] 22 LIGHT • Objects which emit light are called _________________ objects. • Objects which do not emit light themselves but reflect the light of luminous sources, are called _______________________________ objects. • We see things because rays either come directly from them if they are luminous, or rays coming from luminous sources are reflected by non luminous sources into our eyes. Fill in the table below with the following items: fire, chair, shining mirror, moon, Jupiter, galaxy. Luminous Non-luminous Light rays Light rays represent the direction in which light travels. Light rays may be _________________, _______________________, or __________________________. We use a ray box to produce rays in the lab. a ray box ) 23 REFLECTION OF LIGHT Light is reflected when it falls on a reflecting surface such as a mirror. Complete the diagram below marking, the normal, incident ray, reflected ray, angle of incidence (i), angle of reflection (r). Laws of reflection • The angle of incidence and the angle of reflection are __________________. • The normal, the incident and reflected ray all lie _________________________. This means that they can be drawn on a flat sheet of paper. Example: The table below shows the angles of reflection for different angles of incidence obtained by a student during an experiment using a plane mirror and a ray box. Angle of reflection (r) 10 25 30 40 50 Angle of incidence (i) 10 20 30 40 50 • Plot a graph of angle r (y-axis) against angle i (xaxis). • When the angle of incidence is 00 , the angle of reflection is ___________. • What should be the value of the wrongly read angle of reflection? _____________. Mr. N.Briffa HOD 24 Experiment: Reflection Apparatus: __________________________________________________________________________ Diagram: Method: _________________________________________________________________________________________ _________________________________________________________________________________________ _________________________________________________________________________________________ _________________________________________________________________________________________ Table: Conclusion: _________________________________________________________________________________________ _________________________________________________________________________________________ Not all surfaces are able to reflect very well the light rays falling on them. This is due to the surface itself. The smoother the surface, the better it reflects and the shinier it appears. Angle of incidence (0) Angle of reflection (0) 25 The image in a plane mirror is: What is lateral inversion? The word would be seen as if it were to be seen in a mirror. That makes it more difficult to read. On an ambulance the word ambulance is laterally inverted so that drivers could read it properly when they see an ambulance in their cars’ mirrors. The periscope A periscope makes use of reflection. It consists of two plane mirrors facing each other and placed at an angle of 450 . Periscopes are useful when one cannot see something because of an obstacle. The ones used in submarines use prisms rather than mirrors. Real and Virtual images A ______________ image can form on a screen (e.g. cinema, slide projector, camera). A _____________ image does not form on a screen (e.g. mirror, magnifying lens) • _________________________________________ _________________________________________ • _________________________________________ • _________________________________________ • _________________________________________ Complete the diagrams to show where the image forms. 26 This question is about reflection. A shop sign is seen by a student at P but not by one at Q. a) Draw a ray from the shop sign S which reaches P after reflection at the mirror. Include in your diagram, the incident ray, the reflected ray and the normal. (2 marks) b) Show on the diagram the position of the image of S. (1 mark) c) What can be said about: (i) the image distance and the object distance? _____________________________________________________________________________(1 mark) (ii) the type of image? ____________________________________________________________________________ (1 mark) d) Why does the boy find it difficult to read the sign? ____________________________________________________________________________ (1 mark) e) Why can’t the student at Q see the image? ____________________________________________________________________________ (1 mark) Mr. N.Briffa HOD Theme 3 -The Nature of Waves Mr. N. Briffa B.Ed (Hons.) 27 REFRACTION OF LIGHT (bending of light) When light travels through different substances or media, it changes direction because it changes ______________________. This phenomenon of bending is called _______________________. Which of these is an optically denser medium? (glass, water, air). Which of these is an optically less dense medium? (glass, water, air). When light passes from one medium to another, its speed changes. When light passes from an optically less dense medium (e.g. air) to an optically denser medium (e.g. glass) its speed ____________________ and it is bent or refracted __________________ the normal. When light passes from an optically dense medium (e.g. glass) to an optically less dense medium (e.g. air) its speed ___________________ and it is bent or refracted ___________________ the normal. We can compare this effect to a fast car moving on a road that gets stuck in mud and comes out again. 28 Other facts about Refraction The refractive index (n) Every optical material has its own refractive index (e.g. n for glass =1.5, n for water = 1.33). The greater the refractive index of a material, the more is it able to: a) ________________________________________________________________ b) ________________________________________________________________ A ray is not refracted (bent) when it is enters normally (along the normal). An object under water appears at a different depth. A pencil immersed in water appears bent because of refraction. Which material has the greatest refractive index? Why? _______________________________ _______________________________ _______________________________ _______________________________ 29 Example: As light passes from air to glass its speed decreases from 3 x 108 m/s to 2 x108m/s. Find the refractive index of glass. ___________________________________________________________________________________ • The _____________ depth is the depth at which the object is. • The _____________ depth is the depth at which the image forms and the object appears to be. • The apparent depth is always ___________ than the real depth. Example: A diver is at a depth of 6m. He appears to be at a depth of 4.5m. Find the refractive index of water. ______________________________________________________________________________________ ______________________________________________________________________________________ Diffraction of light http://www.olympusmicro.com/primer/java/diffraction/index.html Light is made up of waves and so can be diffracted when it passes through a slit (gap). This however has to be very narrow (< 1/100mm). This is because light has a very short wavelength. When light passes through the very narrow slit, it spreads or ____________ and produces a central bright fringe of light with alternate dark and bright fringes on each side. If a wider slit is used there is less diffraction. This experiment shows that: a) Light is made up of ____________. b) These waves have a very short _____________________. Refractive index (n) = speed of light in air speed of light in medium Refractive index (n) = real depth apparent depth Light pattern on screen Mr. N.Briffa HOD Theme 3 -The Nature of Waves Mr. N. Briffa B.Ed (Hons.) 30 Total Internal REFLECTION The incident ray is not refracted because it enters the glass block along the _______________. When the angle of incidence is very small, there is a strong refracted ray and a very weak ray that is reflected back into the glass block. As the angle of incidence is increased by moving the ray box, at some point the angle of refraction becomes _________. At this point the angle of incidence is called the _______________________________. When the critical angle is ________________ there is ________________________________________. At some point no light from the torch emerges to the surface. Explain why? ______________________________ ______________________________ ______________________________ ______________________________ ______________________________ Mr. N.Briffa HOD Theme 3 -The Nature of Waves Mr. N. Briffa B.Ed (Hons.) 31 Reflecting Prisms When the ray enters the face PQ it is not refracted as it enters along the ______________. The critical angle of glass is 420 and when the ray hits the side PR, the __________________________ is exceeded and so there is ___________________________________. Periscope (using prisms) One application of total internal reflection is used in this type of periscope which uses _____________ instead of mirrors. Draw the correct position of the lower prism of the periscope. Draw a ray showing its path from the object to the observer. Fibre Optics Another application of total internal reflection is fibre optics. They are used by doctors in procedures such as ________________. They are also used for telecommunications. The light ray is trapped inside the solid optical fibre because each time the ______________ angle of the material is exceeded and there is total internal reflection. They are deliberately thin so that the critical angle would be exceeded more easily. Name three advantages of fibre optics over normal wire cables in carrying information. _______________________________________________________________________________ _______________________________________________________________________________ _______________________________________________________________________________ What are the two conditions needed for total internal reflection to occur? _______________________________________________________ _______________________________________________________ _______________________________________________________ _______________________________________________________ 33 Dispersion White light can be split up into a spectrum of 7 different colours. This phenomenon is called _______________________. Continue the ray diagram to show the path taken by the different colours. Mark on the screen where you think might be infra-red and ultraviolet radiation. Which colour is most refracted? ___________________ Which colour travels fastest in glass? __________________ Lenses Lenses are used in optical instruments (e.g. microscopes, telescopes). There are two types of lenses: convex (converging) lens concave (diverging) lens The convex lens is _______________ at the centre and it bends light _______________________. The diverging lens is ________________ at the centre and it bends light _____________________. The centre of the lens is called the _________________________. The line through C at right angles to the lens is called the _________________________________. The focal point is denoted by the letter F. It is also known as _____________________. The focal length is the distance between the ___________________ and the ________________________________ of the lens. 34 Lenses Ray Diagrams Magnifying Lens The image is: __________________, _____________________, __________________. Projector The image is: __________________, _____________________, __________________. Camera The image is: __________________, _____________________, __________________. Mr. N.Briffa HOD Theme 3 -The Nature of Waves Mr. N. Briffa B.Ed (Hons.) 35 Magnification The magnification m is given by the formulae: or The image distance is the distance between the ________________ and the lens. The object distance is the distance between the ________________ and the lens. Example: Continue the following diagram, marking the image formed and stating its properties. Give a use for the diagram below. Calculate also the magnification by using both formulae. _________________________________________________________________________________________ _________________________________________________________________________________________ _________________________________________________________________________________________ _________________________________________________________________________________________ _________________________________________________________________________________________ _________________________________________________________________________________________ Refer to page 12 to complete the table below Height of image (cm) Height of object (cm) Magnification Magnifying lens Projector Camera m = height of image height of object m = image distance (v) object distance (u) Mr. N.Briffa HOD Theme 3 -The Nature of Waves Mr. N. Briffa B.Ed (Hons.) 36 Experiment: Finding the focal length of a converging lens (approximate method) The lens is moved until rays coming from a distant object (e.g. a window) form a sharp image on the wall (screen). The focal length would be the distance between the ______________ and the ______________________ on the wall. The ray diagram for the above experiment would be the following: The image is: __________________, _____________________, __________________. This method is approximate because the rays coming Mr. N.Briffa HOD from the distant object may not be perfectly parallel. Theme 3 -The Nature of Waves Mr. N. Briffa B.Ed (Hons.) 37 Experiment: Finding the focal length of a convex lens (accurate method) Light from the lamp passes through the hole in the screen and is refracted by the lens onto the mirror. The mirror reflects the light back to the convex lens producing an image of the hole with crosswires on the screen. The distance between the image and the lens is equal to the focal length of the lens. Power of a convex lens If a convex lens is thick it will be more able to bend parallel rays of light over a short distance. Therefore the shorter the focal length, the greater the power of the lens. Which of the lenses shown has the greatest power A, B or C? Why? ___________________________________________________ ____________________________________________________________ _____________________________________________________________ 38 Object on F: No image forms in this case. Object on 2F The image is: __________________, _____________________, __________________. Example: A slide is placed 8cm away from a convex lens of focal length 12cm. Draw a ray diagram to scale to show how the image forms. State the characteristics of the 39 Mr. N.Briffa HOD Theme 3 -The Nature of Waves Mr. N. Briffa B.Ed (Hons.) 40 Mr. N.Briffa HOD Linear Motion – Theme 1 – On the Move Mr. N. Briffa B.Ed (Hons.) 1 • When a car keeps moving at the same speed, we say that the car is moving at constant or uniform __________________. • If the driver increases the speed of the car at a constant rate, we say that there is a constant or uniform ______________________. • If the driver decreases the speed of the car at a constant rate, we say that there is a constant or uniform ______________________. Average Speed = Total Distance Total Time This formula can be used either: • To find the average speed of an object. • When an object is moving at constant speed. • It CANNOT be used to find the speed at a point, if the object is accelerating or decelerating. Example : An athlete runs a 40 km race in 90 minutes. Find his speed in km/h and in m/s. ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ Symbol Unit Initial velocity Final velocity Time Acceleration/Deceleration Distance When an object is stationary (at rest) or moves at constant speed, its acceleration is ___________. Acceleration is a vector quantity as it has ______________________ and _________________. Equations of motion 1) v = u + at or a = (v-u) t 2) s = (u+v) x t 2 3) s = ut + ½ a t2 4) v2 = u2 + 2as Mr. N.Briffa HOD Linear Motion – Theme 1 – On the Move Mr. N. Briffa B.Ed (Hons.) 2 Example 1: A sprinter increases his speed from 2m/s to 6m/s in 8 seconds. Find: a) his acceleration. b) the distance travelled. ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ Example 2: A car moving at a speed of 20 m/s is decelerated to rest in 4 seconds. Find: a) its deceleration b) the distance travelled. ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ Example 3: A car starts from rest and is accelerated at 5m/s2 for 8 seconds. Find: a) its final velocity. b) the distance travelled. ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ Example 4: A boy starts from rest and completes a 200 m race in 20 seconds. Find: a) his final velocity. b) his average speed. c) his acceleration. ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ Mr. N.Briffa HOD Linear Motion – Theme 1 – On the Move Mr. N. Briffa B.Ed (Hons.) 3 Example 5: An athelete runs a 100m race. He takes 5 seconds to cover the first 30m. If he continues to run the rest of the race at constant speed, find: a) his final velocity after 30m. ________________________________________________________________________________________ ________________________________________________________________________________________ b) his acceleration. ________________________________________________________________________________________ ________________________________________________________________________________________ c) the total time to run the race. ________________________________________________________________________________________ ________________________________________________________________________________________ Thinking and Braking distance The thinking distance is the ______________ moved by the car while the driver is ______________. The braking distance is the ______________ moved by the car while the driver is _______________. During the thinking distance we assume the car moves at ____________________________. TOTAL STOPPING = THINKING + BRAKING DISTANCE DISTANCE DISTANCE What affects the thinking distance? __________________________________________________________ What affects the braking distance? ___________________________________________________________ 4 Example: A car is moving at 15m/s. The driver sees a child standing in the middle of the road and takes 0.6seconds to apply the brakes. If the car stops in a further 4 seconds. Find: a) the thinking distance ________________________________________________________________________________________ b) the deceleration of the car. ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ c) the braking distance. ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ d) the total stopping distance. ___________________________________________________ Mr. N.Briffa HOD _____________________________________ Linear Motion – Theme 1 – On the Move Mr. N. Briffa B.Ed (Hons.) 5 Example: A driver is driving his car at a speed of 10m/s. A child crosses the road and while the driver reacts, the car moves a distance of 5m. The car is then brought to rest 6 seconds later. Find: a) the thinking time. ________________________________________________________________________________________ b) the deceleration of the car. ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ c) the braking distance. ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ d) the total stopping distance. ___________________________________________________. _____________________________________ 6 Velocity time graphs A motorcycle moves at the same speed of 20m/s for 6 seconds. The graph shows that it is moving at _________________________ or ____________________________. A car is driven from ___________ and its speed is increased uniformly by 5m/s every second. The car is moving with a uniform ____________________ of 5m/s2 . The speed of a car is decreased uniformly from ________ to _______ in ____ seconds. The car makes a uniform ____________________. Mr. N.Briffa HOD Linear Motion – Theme 1 – On the Move Mr. N. Briffa B.Ed (Hons.) 7 Example 1: A car moves at a constant speed of 20m/s for 10 seconds. It is decelerated to rest in a further 4 seconds. Sketch a velocity time graph and find: a) the deceleration. b) the total distance travelled. ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ Example 2: The speed of a car is increased from 4m/s to 12m/s in 10 seconds. Sketch a velocity time graph and find: a) the acceleration. b) the total distance travelled. ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ Example 3: A car moves at a speed of 15m/s for 10 seconds. Its speed is decreased to 5m/s in a further 3seconds. Sketch a velocity time graph and find: a) the deceleration. b) the total distance travelled. ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ 9 Distance time graphs Consider a man standing at a certain distance from a wall. As time goes by, the distance between a man and a wall remains _____m. This means that the man is _____________. The man is standing against the wall. Every second the man is moving a distance of ________ AWAY FROM the wall. He is moving with a constant speed of ___________. The man is standing _______ away from the wall. He starts to move with constant speed TOWARDS the wall. After 6 seconds he is __________________. Mr. N.Briffa HOD Linear Motion – Theme 1 – On the Move Mr. N. Briffa B.Ed (Hons.) 10 Example: Using the distance time graph shown find the speed of the moving object shown. _________________________________________________ _________________________________________________ _________________________________________________ _________________________________________________ _________________________________________________ 12 Acceleration due to gravity (g) If the marble, the iron ball and the feather are dropped from the same height, the marble and the iron ball fall and hit the ground exactly at the same time. This is because on Earth all objects fall with an acceleration (g) of 9.8m/s2 . The feather falls with less acceleration because of ________ ________________. This is negligible in the case of the marble and the iron ball. Experiment: Air is extracted by means of a vacuum pump. A _____________ is created inside the tube. The marble and feather inside the glass tube fall in the same way. In a vacuum, there is no _____ ________________ since no air is present. Therefore, the feather and the marble fall with an acceleration of 9.8m/s2 . This is called ‘g’, the acceleration due to _____________ or acceleration of __________________. Usually when we work problems, ‘g’ is taken to be 10m/s2 . Object dropped from 1m height Stone of mass 0.1kg Stone of mass 5kg Stone of 5kg in vacuum Feather Feather in vacuum Small parachute Same parachute in vacuum Typical acceleration For falling objects which are DROPPED : ( u = 0 m/s ) s=½ g t 2 Example 1 : A ball is dropped from a certain height and takes 5 seconds to reach the ground. From which height was it released? What have you assumed in your calculation? ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ 13 Example 2 : A stone is dropped from a height of 15m. Find the time it takes to hit the ground. What have you assumed? ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ Experiment: Measuring ‘g’ the acceleration due to gravity • When the switch is on position 1, the ________________ attracts the iron ball. • When the switch is moved quickly to position 2, the iron ball __________ and the _____________ starts. • The timer stops counting when the ____________ hits the _____________. • The distance fallen is measured with a __________________. • Using the equation: s=½ g t 2 g = 2 s t 2 For example, if the distance fallen is 1 m and the time recorded is 0.45seconds: g = 2 x 1 = 9.88m/s2 (0.45) 2 Mr. N.Briffa HOD 1 Inertia is the reluctance (laziness) to change _____________________________. The greater the __________ of an object, the greater its inertia. Examples of INERTIA in everyday life: Inertia makes it difficult to run fast the first few metres of a race. The athlete’s body is at rest and does not want to change its state of motion. It wants to remain at rest. However, once the athlete gains speed, it would be difficult to stop, as the body does not want to change its state of motion. It wants to keep on moving. When the sheet of paper is pulled rapidly, the coin falls into the glass. The coin is at rest and does not want to change its state of motion. It is hard to push a stationary object. The van is at rest and wants to remain at rest. It does not want to change its state of motion. When a car stops suddenly, the body moves forward due to inertia. Seatbelts prevent the forward motion caused by inertia. Airbags also help to prevent injury. Inertia can kill. Website about crashtests: http://regentsprep.org/regents/physics/phys01/accident The Resultant Force (Unbalanced Force) Newton’s 1st law: (The law of INERTIA) If there are no external forces: • an object that is at rest will stay ___________. • a moving object will continue to move _________________. When a fan is switched on, it rotates very slowly in the first few seconds. It is reluctant to start moving. When it switched off, it continues to rotate for some time as it is again reluctant to change the state of motion. Isaac Newton 1643-1727 Mr. N.Briffa HOD Newton’s Laws of Motion – Theme 1 – On the move Mr. N. Briffa B. Ed. (Hons) 2 Example 1: _______________________________ In this case the object would __________________ to the _____________. Example 2: Name the forces: F1 __________________________________ F2 __________________________________ F3 __________________________________ Force F1 is equal to 6,000N, force F2 is equal to 1,000N and F3 is equal to 2,000N. Find the resultant force acting on the car in this case. ________________________________________________________________________________________ ________________________________________________________________________________________ In this case the car would __________________ to the _____________. Example 3: The resultant force in this case is 0 N. In this case the object can be either: a) _________________________________ or b) __________________________________ Mr. N.Briffa HOD Newton’s Laws of Motion – Theme 1 – On the move Mr. N. Briffa B. Ed. (Hons) 3 Find the resultant force and state the type of motion in each case. Resultant Force = ________________________________ Type of motion = ________________________________ Resultant Force = ________________________________ Type of motion = ________________________________ Resultant Force = ________________________________ Type of motion = ________________________________ Resultant Force = ________________________________ Type of motion = ________________________________ Resultant Force = ________________________________ Type of motion = ________________________________ Suggest a value for the air drag if the car is: a) moving at constant speed. ______________________________________ b) accelerating. ______________________________________ Mr. N.Briffa HOD Newton’s Laws of Motion – Theme 1 – On the move Mr. N. Briffa B. Ed. (Hons) 4 Example 1: Find the resultant force acting on an object having a mass of 6kg and which is being accelerated at 5m/s2 . ___________________________________________________________________________________ Example 2: If the object has a mass of 3kg, find: a) resultant force __________________________ b) acceleration _____________________________________________________________________ Example 4: A rope is used to lift an object of mass 30kg. a) Name the force caused by the mass of the object and label it in the diagram. ____________________________________________________________________ b) What is the value of the tension when the object is stationary? ____________________________________________________________________ c) What is the value of the tension when the object is lowered at constant speed? ____________________________________________________________________ d) What is the value of the tension when the object is lifted at constant speed? ____________________________________________________________________ e) Suggest a value for the tension when the object is accelerated upward. _____________________________________________________________________ Newton’s 2nd law: ( F = m a ) The resultant force is the product of ________ and _________________. F = m a (N) (kg) (m/s2) 5 Example 3: A van is travelling on a horizontal road at constant velocity. The forces acting on the van are shown in the diagram below. The force F produced by the engine is 500N. a) Name the force P and calculate a value for it. _____________________________________________ b) Name the force Q and calculate a value for it. _____________________________________________ c) Calculate the mass of the van. __________________________________________________________ The engine force F is suddenly increased to 1200N. Calculate: d i) the resultant force driving the van forward assuming there is no change in Q. _____________________________________________________________________________________ ii) the acceleration of the van. _____________________________________________________________________________________ Definition: Momentum is the product of _____________ and ___________________. S.I. units: kg m/s Other units: kg cm/s Momentum is a ________________ quantity as it has magnitude and direction. Example: Find the momentum of a car of mass 2000kg moving at 25m/s. ________________________________________________________ Which one has more momentum in each case? (Use the signs >, < or =) Car moving at 20m/s. Same car moving at 35m/s. Car moving at 20m/s. Truck moving at 20m/s. Car moving at 20m/s. Aeroplane at rest on the runway. Car of mass 1000kg moving at 20m/s. Truck of mass 5000kg moving at 4m/s. Momentum = mass x velocity (kg m/s) (kg) (m/s) Mr. N.Briffa HOD Newton’s Laws of Motion – Theme 1 – On the move Mr. N. Briffa B. Ed. (Hons) 6 Example 4: When accidents happen at sea, injured persons are often rescued by helicopter as shown in the diagram. a) If the mass of the helicopter is 1500kg, what upward force must be produced by the rotation of the rotor blades to keep the helicopter at constant height? Explain. ________________________________________________ ________________________________________________ ________________________________________________ b) The injured person and the rescuer of combined mass 120kg, have belts attached to their waists. A rope, which is hooked to these belts, is then wound up by an electric motor in the helicopter. After a brief acceleration, the two people rise vertically at a constant speed of 10m each minute. i) What is the tension in the rope as it is drawn into the helicopter at constant speed? _____________________________________________________________________________________ ii) Is the tension in the rope during the acceleration likely to be greater than, less than or equal to your answer in part b i)? Explain. _____________________________________________________________________________________ _____________________________________________________________________________________ iii) The acceleration while they are being lifted is 0.5m/s2 . Calculate the value of this tension. _____________________________________________________________________________________ _____________________________________________________________________________________ c) Calculate the power of the motor when the people at the end of the rope are rising at a constant speed. (Assume the process is 100% efficient). _____________________________________________________________________________________ _____________________________________________________________________________________ Mr. N.Briffa HOD Newton’s Laws of Motion – Theme 1 – On the move Mr. N. Briffa B. Ed. (Hons) 7 Example 5: A car starts from rest and reaches a speed of 20m/s in 5 seconds. If it has a mass of 1500kg, Find: a) the acceleration. _____________________________________________________________________ b) the resultant force. ___________________________________________________________________ c) initial momentum. ___________________________________________________________________ d) final momentum. ____________________________________________________________________ e) change in momentum. ________________________________________________________________ Example 6: A driver of mass 80kg loses control of his car which is moving at 10m/s, and crashes into a wall. He comes to rest in 0.5 seconds. Find: a) the deceleration of the driver ___________________________________________________________ b) the average decelerating force of the seatbelt on the driver if it is to hold him firmly in his seat. _____________________________________________________________________________________ Example 7: High flying birds such as mallard ducks could be a source of danger to aircrafts because if they collide with the windscreen, the resulting impact could cause serious damage to the aircraft. Fifteen mallard ducks each of mass 1kg, travelling at 20m/s collide with an aeroplane. The aeroplane of mass 2000kg is travelling with a velocity of 200m/s in the opposite direction. a) Calculate the momentum of the aeroplane before the collision. ________________________________ b) Calculate the momentum of the ducks before the collision. ___________________________________ c) Calculate the total momentum of the plane and mallard ducks before collision. ___________________ ____________________________________________________________________________________ An object moving to the right has a ________________ momentum. An object moving to the left has a _________________ momentum. Mr. N.Briffa HOD Newton’s Laws of Motion – Theme 1 – On the move Mr. N. Briffa B. Ed. (Hons) 8 d) One of the mallard ducks hits the aeroplane windscreen. Calculate the impact force on the windscreen, if the collision lasts for 0.001seconds. ___________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ e) The aeroplane windscreen is designed to withstand an impact force of 5.0 x 104N. Will it break or not? ________________________________________________________________________________________ Newton’s 2nd law : (Everyday examples) F = m a and a = (v – u) and so F = m (v – u) t t or F = mv - mu = (change in momentum) t time Seatbelt What is the use of a seatbelt? _______________________________________________________________ Why should it stretch a little bit? _______________________________________________________________ __________________________________________________ Airbag How does an airbag help to prevent injury? __________________________________________________ __________________________________________________ Crumple zones What are crumple zones? _______________________________________________ _______________________________________________ Catching a ball Why should the hand be moved slightly backward? _______________________________________________ _______________________________________________ Flexing knees after jumping Why should we flex our knees when jumping? _______________________________________________ _______________________________________________ Mr. N.Briffa HOD Newton’s Laws of Motion – Theme 1 – On the move Mr. N. Briffa B. Ed. (Hons) 9 Packaging material Packaging material is designed in a way to ______________ the time of _______________ and so protect fragile objects inside. Hammering a nail When a nail is hammered in a wooden block, the impact should last a ________ time, so that the force created is _____________________. If both cardboard tubes are released from a height of 3m, the egg which is resting on the crumpled aluminium foil would not break. Explain why. ___________________________________________________________ ___________________________________________________________ ___________________________________________________________ ___________________________________________________________ Example 8: a) A car advert specifies that the car can reach a speed of 25m/s from rest in 18 seconds. Calculate the acceleration of the car. ________________________________________________________________________________________ ________________________________________________________________________________________ b) Cars are tested for safety during accidents in special laboratories. i) When a car crashes into a wall, the person continues to move forward. Explain why this happens. ____________________________________________________________ ____________________________________________________________ ii) Seatbelts are slightly elastic and stretch slightly before stopping the passenger from moving forward. What is the advantage of this? ________________________________________________________________________________________ ________________________________________________________________________________________ iii) Airbags are designed to open in front of passengers in the case of an accident. Suggest two ways in which an airbag can decrease the force of impact. ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ 10 The air track Finding the average speed of a glider on an airtrack The formula SPEED = DISTANCE is used. TIME When the front of the glider reaches the photodiode, the timer ___________. When the back part of the glider passes the photodiode, the timer ____________. The distance is equal to the length of the glider and is measured with a metre ruler. Example: A glider has a length of 10cm. It takes 0.4 seconds to pass in front of the photodiode. Find the average speed of the glider. ___________________________________________________. _____________________________________ 11 On a LEVELLED airtrack the glider will move at CONSTANT SPEED when slightly pushed When the glider is slightly pushed the time recorded on each timer is the _________. This means that the glider is neither _________________ nor ___________________. It is moving at __________ ______________. The speed in each case can be found by using Speed = Distance/Time. The air track is levelled by using a ________ _______________. ________________________________________________________________________________________ According to Newton’s second law: F = m a and so a = F m a α F acceleration and Force are ____________ proportional. ( the greater the force the ___________ the acceleration). e.g The harder you push a shopping trolley the more it will accelerate. a α 1 acceleration and mass are ____________ proportional. m ( the greater the mass the ____________ the acceleration). e.g The greater the mass of the shopping trolleys the less they will accelerate. 12 Experiment: The GREATER the Force the GREATER the acceleration ( a α F ) A weight (force) is used to pull the glider. The glider is released and its acceleration is noted. This is repeated several times by adding more ___________________ to increase the force. It is noted that as the force to pull the glider is increased the ______________________ increases. So acceleration and force are ____________________ proportional. Table of results: Force (N) Acceleration (m/s2 ) 13 Experiment: The GREATER the Mass the SMALLER the acceleration ( a α 1/m ) A weight (force) is used to pull the glider. The glider is released and its acceleration is noted. This is repeated several times by adding more ___________________ on top of each other to increase their ____________. It is noted that as the mass of the gliders is increased, the acceleration ____________________. So acceleration and mass of gliders are ____________________ proportional. Table of results: Mass of Gliders (kg) Acceleration (m/s2) 14 Terminal Velocity The feather is dropped from a certain height. Initially its speed increases and so there is an ______________________. At this point the _____________ of the feather is greater than the _________ _________________. However the air resistance increases until it is equal to the ______________ of the feather. At this point the resultant force is equal to ___ N. The feather does not accelerate any longer and reaches it maximum constant velocity also known as ____________ ______________. Determine whether each of the following will reach terminal velocity. A table tennis ball falling a height of 30m. Yes A raindrop. An iron ball falling a distance of 5m. A parachutist falling down. A feather falling a height of 20cm. An iron ball falling a distance of 5m in oil. Simulation terminal velocity: http://www.physicsclassroom.com/mmedia/newtlaws/sd.html Newton’s 3 rd law: For every ___________ there is an equal and opposite _________________. Momentum is the product of _____________ and ____________________. The SI unit is _____________. Types of collision: An ___________________ collision occurs when the objects STICK TOGETHER after colliding. An ___________________ collision occurs when the objects SEPARATE after colliding. An ___________________ occurs when two combined objects separate by moving in opposite directions. State whether each of the following is an inelastic collision, an elastic collision or an explosion. Inelastic collision Elastic collision Explosion Toy car A hits toy car B and they move on together. Toy car A hit toy car B which is at rest. A stops and B moves off. Toy car A and B are held together by a spring. They are released and then they move in opposite directions. Firing a gun. Stepping off a skateboard. Rubber ball hitting the floor. Plasticine hitting the floor. A white billiards ball hitting a red one. Hot gases coming out of a rocket. Cork shooting high after opening champagne. Kicking a ball. An ice skater skating towards another one, moving on together after colliding. A bumping car hitting a wall. Jumping into mud. Inflating a balloon without tying a knot and letting it go of. The Law of conservation of Momentum: The total momentum ______________ collision is equal to the total momentum _______________, provided that there are ____________________________________. (e.g. friction). 2 Example: (Inelastic Collision) A trolley A of mass 2kg moving at 3m/s collides with a stationary trolley B of mass 3kg. If the trolleys move on together after impact, find their common velocity. Total Momentum Before impact = Total Momentum After impact m1v1 + m2v2 = (m1+m2) v3 ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ The same question can be asked as follows: a) Find the momentum of trolley A before collision. ______________________________________________ b) Find the momemtum of trolley B before collision. ______________________________________________ c) What is the total momentum before collision? _________________________________________________ d) What is the total momentum after collision? __________________________________________________ e) Find the common velocity after the collision. ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ f) Find the total K.E. before the collision. ______________________________________________________ g) Find the total K.E. after the collision. _______________________________________________________ h) Find the K.E. ‘lost’ during the collision. _____________________________________________________ i) Is K.E. conserved in this case? Why? _______________________________________________________ So only _________________ is conserved. _________ is not conserved in an inelastic collision. Mr. N.Briffa HOD Momentum and Collisions - Theme 1 – On the Move Mr. N. Briffa B.Ed (Hons.) 3 This question is about momentum and collisions. a) Define the momentum of an object and state its units. ______________________________________________________________________________________(3) b) The diagram shows an experiment on collisions between trolleys. Both trolleys have a mass of 2kg. Trolley A moving at 1.5m/s collides and sticks to trolley B which is at rest. i) What is the momentum of A before collision? _____________________________________________________________________________________ (1) ii) What is the momentum of B before collision? _____________________________________________________________________________________ (1) iii) What is the total momentum before the collision? _____________________________________________________________________________________ (1) iv) What is the total momentum after? Explain. _____________________________________________________________________________________ (3) v) What is the velocity of the trolleys after the collision? _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ (2) vi) What is the kinetic energy of A before the collision? _____________________________________________________________________________________ _____________________________________________________________________________________ (3) vii) What is the total kinetic energy of A and B after the collision? _____________________________________________________________________________________ _____________________________________________________________________________________ (2) viii) Can you explain the difference between the answers in vi) and vii)? _____________________________________________________________________________________ (4) 4 Example: (Elastic Collision) A trolley A of mass 4kg moving at 9m/s collides with a stationary trolley B of mass 2kg. If after colliding, trolley A moves at a speed of 3m/s, find the speed at which trolley B moves off. Total Momentum Before impact = Total Momentum After impact m1v1 + m2v2 = m1 v3 + m2v4 ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ Example: A sphere X of mass 4kg moving a 1m/s collides with an identical sphere Y which is at rest. If X stops: a) Find the speed of sphere Y after collision. b) Is K.E. conserved in this case? ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ So both ______________ and ________ are conserved in a perfectly elastic collision. Momentum and Collisions - Theme 1 – On the Move Mr. N. Briffa B.Ed (Hons.) 5 Example: A minibus of mass 2000kg travelling at 10m/s collides headon with a car of mass 1200kg and which is moving at 30m/s in the opposite direction. If the two vehicles stick together on impact, find their common velocity and state in which direction they move. ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ Explosions When an explosion occurs the two objects separate and have an equal and opposite momentum. Explosions are related to Newton’s 3rd law which states that for every _______________ there is an equal and opposite ________________. The total momentum before and after an explosion is 0 kgm/s. Total Momentum before explosion = Total momentum after explosion 0 = - m1v1 + m2v2 Mr. N.Briffa HOD Momentum and Collisions - Theme 1 – On the Move Mr. N. Briffa B.Ed (Hons.) 6 Example 1: The velocity of a bullet of mass 5g after being fired is 60m/s. If the mass of the gun is 4kg, find the recoil velocity of the gun. Momentum bullet = Momentum gun m1v1 = m2v2 ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ The same question can be asked as follows: a) What is the total momentum before the gun is fired? Why? ________________________________________________________________________________________ b) What is the total momentum after the gun is fired? Why? ________________________________________________________________________________________ c) Find the momentum of the bullet after it is fired. ________________________________________________________________________________________ d)What is the momentum of the gun after it fires the bullet? Explain. ________________________________________________________________________________________ e)Find the recoil velocity of the gun. ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ Example 2: A man of mass 70kg jumps out of a boat with a speed of 3m/s. The boat of mass 300kg moves backwards. a)Why does the boat move backwards? ________________________________________________________________________________________ b)Find the speed at which the boat moves backwards. ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ 7 Example 3: The diagram shows two stationary trolleys separated by a compressed spring and held together by a thread. The mass of trolley A is 2kg and that of B is 1kg. When the thread is cut, the trolleys move rapidly apart. a) Which force is causing the movement of the trolleys? ________________________________________________________________________________________ b) What is the total momentum before and just after the thread is cut? Why? ________________________________________________________________________________________ ________________________________________________________________________________________ c)If trolley A moves off with a speed of 0.25m/s, calculate the speed at which trolley B moves off. ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ Example 4: The diagram shows two girls on roller skates. Nicole has a mass of 25kg while Roberta has a mass of 20kg. They are initially at rest. a) What is the total momentum before they push each other? Why? ________________________________________________________________ b) Is momentum a scalar or vector quantity? Why? ________________________________________________________________ c) Soon after they push each other, Nicole moves at a speed of 2m/s. Calculate her momentum. ________________________________________________________________________________________ d) What is the momentum of Roberta at this point? Why? _______________________________________________________________________________________ _______________________________________________________________________________________ e) Find the speed at which Roberta starts to move. ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ________________________________________________________________________________________ 8 Experiment: To prove the LAW OF CONSERVATION OF MOMENTUM ( for an inelastic collision) Method: Some plasticine is attached to glider 1 which is then slightly pushed. It passes in front of the first photodiode. It then hits glider 2 which is at ___________. The two gliders ______________________________ and pass in front of the second photodiode. Results: m1 is the mass of the ____________ glider. m2 is the mass of the _____________ glider. v1 is the velocity of the _____________ glider BEFORE collision = length of glider 1 Time of timer 1 v2 is 0m/s because glider 2 is at __________ BEFORE collision. v3 is the velocity of ____________ trolleys AFTER collision = length of BOTH gliders Time of timer 2 Calculation: Total momentum before = m1v1 + m2v2 Total momentum after = (m1+m2) v3 Precautions: • The air track is leveled with a ___________________________. • A constant flow of air is checked to be present so that there is no __________________ between the gliders and the airtrack. Conclusion: The total momentum before collision is found to be equal to the total momentum after and so momentum is _________________________ in an inelastic collision. 1 THE STRUCTURE OF THE ATOM • All matter is made up of very small particles called ___________. • The centre of the atom is called the _____________. • The nucleus contains ___________ and ____________. Moving on the outer surface, there are very small particles called _________________. • A proton has a ______________ charge. • An electron has a _____________ charge. • A neutron is neutral and has _______________. In an atom the NUMBER OF ELECTRONS = NUMBER OF PROTONS. Therefore the atom is overall uncharged. It is ___________________. However, an atom may become charged when it loses or gains electrons. When rubbed with a cloth, POLYTHENE becomes _____________________ charged. When rubbed with a cloth, PERSPEX (or cellulose acetate) becomes ___________________ charged. This atom has a lack of electrons. It lost ___ electrons. So it is ______________ charged. This atom has an excess of electrons. It gained ___ electron. So it is ______________ charged. Only the electrons can move . The protons and neutrons are ‘imprisoned’ in the _____________. Law of charges LIKE charges (- - or ++) ___________, UNLIKE charges (+ -) ____________. Mr. N.Briffa HOD Electricity – Theme 5 – Part 1 -Electricity in the Home Mr. N. Briffa B. Ed. (Hons) 2 Charging by FRICTION If a polythene strip is rubbed against a cloth, electrons would move from the _____________ to the _________________. The polythene becomes _____________ charged because it ends up with an ______________ of electrons. The cloth becomes ___________________ charged because it ends up with a _____________ of electrons. If a perspex strip is rubbed against a cloth electrons would move from the _____________ to the _______________. The perspex becomes _____________ charged because it ends up with a ____________ of electrons. The cloth becomes ___________________ charged because it ends up with an _____________ of electrons. Charged objects lose their charge faster in wet and humid conditions. Result Positive Positive Negative Negative Positive Negative Positive Neutral Negative Neutral Neutral Neutral Mr. N.Briffa HOD Electricity – Theme 5 – Part 1 -Electricity in the Home Mr. N. Briffa B. Ed. (Hons) 3 CONDUCTORS AND INSULATORS Some materials allow current to flow through them. They are called _____________. Conductors have __________ electrons. The greater the number of free electrons, the better the conductor. Good conductors of electricity include gold, silver, copper and aluminium. Some materials do not allow current to flow through them. They are called ________________. They have loosely bound electrons called _________ electrons. _____________ are bad conductors of electricity and have strongly bound electrons. Wood, plastic, rubber, and polystyrene are bad conductors of electricity. Conductor/Insulator Bulb lights (yes/no) Wooden bar Plastic ruler Metal ruler Earthing: If a charged metal object is earthed with a conductor it becomes ________________. _______________________________ _______________________________ _______________________________ _______________________________ _______________________________ _______________________________ _______________________________ _______________________________ 5 Andre Ampere 1775 -1836 Charge and Current • The amount of electrons present on the sphere is called ________________. • Current is the __________ of flow of charge (how many electrons flow in one second). Symbol Unit Example Charge Current Q = I t Charge = Current x time (Coulombs) (Amps) (seconds) Example : Find the amount of charge present if a current of 5A flows every 2 minutes. ________________________________________________________________________________________ Electrical components Picture Symbol Use Cell Battery Power supply (d.c) When a negatively charged sphere is earthed as shown, __________ flow from the sphere to earth. The ________________ gives a reading while the electrons are flowing down. This simple experiment shows that current is a flow of ____________. The flow of current lasts for a very short time until the sphere becomes _____________. The greater the charge on the sphere, the greater Bulb/Lamp Open switch Closed switch Ammeter Voltmeter Multimeter Resistor Variable resistor (rheostat) Conventional current and Electron flow Before electrons were discovered, scientists believed that current flowed from the positive to the negative terminal of a cell. Later, they realized it was a mistake. It was too late to redefine all the electrical Physics, so the inconvenience holds to this day. In the coursework we will use __________________________. Conventional current is the way current flows from the ______________ to the ______________ terminal of the cell. Electron flow is the way electrons flows from the _____________ to the Mr. N.Briffa HOD _______________ terminal of the cell. Electricity – Theme 5 – Part 1 -Electricity in the Home Mr. N. Briffa B. Ed. (Hons) 7 Alessandro Volta 1745 -1827 Voltage The difference in the number of electrons between the terminals of a cell is called ____________. The greater the difference, the greater the voltage. For ___________ to flow, voltage needs to be present. If there is no voltage there can be no current flowing. E.m.f stands for ________________________________ and is the voltage across a cell. P.d stands for ___________________________ and is the voltage across the circuit. Both e.m.f. and p.d . are measured in _____________. E = Q V Energy = Charge x Voltage (Joules) (Coulombs) (Volts) Example: Find the electrical energy used if the charge is 5C and the potential difference is 12V. ________________________________________________________________________________________ These 3 bulbs are connected in _________. If one bulb ___________, the others would ________________. These 2 bulbs are connected in ____________. If one bulb ___________, the others would ___________________. Georg Ohm 1789 -1854 Resistance The opposition to current flow is called __________________. Resistance depends on: a) __________________ ( the thicker the wire, the _______________ the resistance). b) ___________________ ( the longer the wire, the ____________ the resistance). c) ___________________ ( the higher the temperature, the ____________ the resistance). d) the type of material. (eg. copper, silver, iron, gold). Resistance is measured in ohms (Ω). For example, we say a wire has a resistance of 6 Ω. The best conductors (e.g. gold) have the _________________ resistance. Insulators have an infinitely ______________ resistance. Measuring instruments Current is measured by using an _______________. It is always connected in ____________ and has a _______________ resistance. Voltage is measured by using a ___________________. It is always connected in _________________ and has a _____________ resistance. Label the measuring instruments in each diagram. The brightness can be controlled by using the _____________________ (rheostat). High resistance - _______ current - Lamp is __________. Low resistance - _______ current - Lamp is _________. 9 V = I Voltage = Current x Resistance (Volts) (Amps) (Ohms) Example: A current of 0.5A passes through a resistor of resistance 10Ω. Find the voltage across it. ________________________________________________________________________________________ EQUATIONS: 1. Q = It 2. E = Q V 3. V = I R 4. E = V I t 5. E = V2 t R 6. E = I2 Rt Finding the RESISTANCE of a metal wire To find the resistance of a metal wire we need to know its voltage and its current (R= V/I). Example: The p.d. across a resistor is 2V and a current of 4A flows through it. Find: a) the resistance of the resistor. ___________________________________________________________ _________________________________________________________ b) the energy dissipated by the resistor as heat in 3 minutes. ___________________________________________________________ ___________________________________________________________ ___________________________________________________________ The voltage is noted on the ______________. The current is noted on the ______________. The equation R = V/ I is used. The resistance of any component can be found Mr. N.Briffa HOD in this way. (e.g filament lamp, resistor etc.) Electricity – Theme 5 – Part 1 -Electricity in the Home Mr. N. Briffa B. Ed. (Hons) 10 OHM’S LAW OHMIC and NON-OHMIC conductors • __________________ conductors obey Ohm’s law and the graph obtained is a straight line. Voltage and current are ______________ proportional. (eg. metals, constantan wire) • __________________ conductors do not obey Ohm’s law and the graph obtained is not a straight line. Voltage and current are not directly proportional (eg. filament lamp, themistor, diode). _____________ is directly proportional to ____________ as long as the _______________ remains constant. Experiment: The voltage is noted on the ________________. The current is noted on the ________________. This is repeated several times by changing the current with the ___________________________. Table: Voltage (V) Current (A) Precaution: _______________________________ _________________________________________ _________________________________________ Graph: The gradient of the graph (∆Y/∆X) gives the ______________. Metal Filament lamp Thermistor Mr.H.Rushema HOD Electricity – Theme 5 – Part 1 -Electricity in the Home Mr. N. Briffa B. Ed. (Hons) 11 Example 1: Example 2: Example 3: Complete the diagrams to show how voltage may divide in series and parallel circuits a) Find the total resistance _____________________________ b) Find the total current flowing _________________________ c) Find the voltage across the 6Ω resistor. ___________________________________________________ ___________________________________________________ d) Find the voltage across the 2Ω resistor. ___________________________________________________ ___________________________________________________ a) Find the total resistance _____________________________ b) Find the total current flowing _________________________ c) Find the voltage across the 5 Ω resistor. ___________________________________________________ ___________________________________________________ d) Find the voltage across the 1Ω resistor. ___________________________________________________ ___________________________________________________ a) Find the voltage across the 4 Ω resistor. _________________ ___________________________________________________ b) Find the voltage across R ____________________________ c) Find the resistance of R.______________________________ ___________________________________________________ ___________________________________________________ Mr. N.Briffa HOD Electricity – Theme 5 – Part 1 -Electricity in the Home Mr. N. Briffa B. Ed. (Hons) 12 Example 4: Example5: Example 6: Example 7: a)Find the voltage across the 12Ω resistor . ___________________________________________________ b)Find the voltage across the 6Ω resistor . ___________________________________________________ c) Find the current in the 12Ω resistor. ___________________________________________________ ___________________________________________________ d) Find the current in the 6Ω resistor. ___________________________________________________ e) Which resistor has more current flowing through it? Why? ___________________________________________________ ___________________________________________________ a) Find the voltage across AB. ___________________________________________________ b) Find the voltage across BC. ___________________________________________________ c) Find the current in the 8Ω resistor. ___________________________________________________ ___________________________________________________ d) Find the current in the 2Ω resistor. ___________________________________________________ a) Find the voltage across AB . __________________________________________ b) What is the voltage across BC? __________________________________________ c) What is the voltage across CD? __________________________________________ d) Find the current in the: i ) 2 Ω resistor ______________________________ ii ) 3 Ω resistor _____________________________ iii) 6 Ω resistor _____________________________ Mr. N.Briffa HOD Electricity – Theme 5 – Part 1 -Electricity in the Home Mr. N. Briffa B. Ed. (Hons) 13 Example 7: Combined resistance of resistors in parallel The combined resistance of resistors in parallel is always less than the resistance of the smallest resistor. a) Find the voltage across AB . _______________________________________________________ b)What is the voltage across BC ? _____________________________________________________ c) Find the current in the 3Ω resistor. _________________________________________________________________________________ _________________________________________________________________________________ d) Find the resistance of R. _________________________________________________________________________________ _________________________________________________________________________________ The total resistance for these resistors in series is ______ Ω For two resistors in parallel the total resistance is found by using the formula: 1 = 1 + 1 so 1 = 1 + 1 = 2 + 3 = 5 R R1 R2 R 6 4 12 12 1 = 5 so R = 12 = 2.4 Ω R 12 5 Electricity – Theme 5 – Part 1 -Electricity in the Home Mr. N. Briffa B. Ed. (Hons) 14 Example 8: a) Find the total resistance of the circuit. ________________________________________________________________________________________ ________________________________________________________________________________________ b) What is the reading on the ammeter? ________________________________________________________________________________________ Example 9: a) Find the total resistance between B and C. ________________________________________________________________________________________ b) Find the total resistance between A and C. ________________________________________________________________________________________ c) Find the current passing through the 3.5 Ω resistor. ________________________________________________________________________________________ d) Find the voltage across AB. ________________________________________________________________________________________ e) What is the voltage across BC? ________________________________________________________________________________________ f) Find the current passing through the 2 Ω resistor. ________________________________________________________________________________________ g) Find the current passing through the 6 Ω resistor. ________________________________________________________________________________________ Electricity – Theme 5 – Part 1 -Electricity in the Home Mr. N. Briffa B. Ed. (Hons) 15 Example 10: Semiconductor components These devices are made up of special material that gives them special properties. Electrical component Symbol Function Diode Allows current to flow in one __________________. L.E.D A diode that can emit _______________________. L.D.R A resistor whose resistance depends on _________________. Thermistor A resistor whose resistance depends on ___________________. The diode: A B The lamp will light in circuit _________. In circuit A, the diode is said to be _______________ ______________. The current can flow through the circuit. In circuit B, the diode is said to be _______________ ______________. The current flowing is negligible (almost no current flows). A current of 1A flows through the 2Ω resistor. a) Find the voltage across the 2 Ω resistor? ___________________________________________________ b)Find the current in the 4 Ω resistor. ___________________________________________________ c) Find the current passing through R. ___________________________________________________ ___________________________________________________ d) Find the resistance of R. ___________________________________________________ ___________________________________________________ Electricity – Theme 5 – Part 1 -Electricity in the Home Mr. N. Briffa B. Ed. (Hons) 16 Protecting equipment using diodes The Light Emitting Diode (L.E.D): A L.E.D is a special diode that emits ____________ when it is forward biased. The uses of a L.E.D: a) ________________________________________________ b) ________________________________________________ Example: A L.E.D has a voltage drop across it of 2V and needs a current of only 0.01A. If it is connected to a 9V supply , find the resistance of a protective resistor which is needed. _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ If the cell is connected as shown in the diagram the radio will work because the diode will be ___________ ______________. If the cell is connected the other way round the radio would not work as the diode would now be __________ ______________. No damage would be done to the components inside the radio. The seven segment display used in alarm clocks makes use of 7 light emitting diodes. Electricity – Theme 5 – Part 1 -Electricity in the Home Mr.H.Rushema 17 A fixed resistor would usually look as shown and would not have any special property apart from decreasing current. However, there are special resistors made up of semi-conductor material that give these resistors special properties. SPECIAL RESISTORS: L.D.R Thermistor The Light Dependent Resistor (L.D.R): A Light Dependent Resistor or (L.D.R) is a special resistor whose resistance varies with the amount of ____________________. It is made up of a special semiconductor material (cadmium sulphide). In the dark it has a very high resistance (e.g. 2MΩ) and in sunlight it has a very low resistance (e.g 100Ω). DARK - _______________ resistance SUNLIGHT - _______________ resistance When will the L.D.R conduct more current? _____________________________________________. Use for an L.D.R: ____________________________________________________ The Thermistor: A thermistor is a special resistor whose resistance varies with ____________________. When cold, it has a very high resistance, while when hot it has a very low resistance. COLD - _______________ resistance HOT - _______________ resistance When will the thermistor conduct more current? _________________________________________. Use for a Thermistor: __________________________________________________ fixed resistor Electricity – Theme 5 – Part 1 -Electricity in the Home Mr. N. Briffa B. Ed. (Hons) 18 The Lightmeter Describe briefly an experiment to find the resistance of a thermistor at 750C When light falls on the LDR, the milli-ammeter gives a reading because current flows. In the dark, the resistance of the LDR is__________________, and the current is __________________. In sunlight, the resistance of the LDR is __________________, and the current is __________________. The greater the amount of light, the ___________ the current flowing through the circuit. Method: When the temperature reaches 750C, the voltage is noted on the _______________ and the current is noted on the _______________. Equation: ________________________________ Precaution: _________________________________________ _________________________________________ _________________________________________