PHYSICS LEVEL 1

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WAVES AND OPTICS TINKHAM QUESTIONS

1. Suppose that a longitudinal wave moves along a Slinky at a speed of 5 m/s. Does one coil of the Slinky moves through a distance of 5 m in one second? Explain.

2. Does the principle of linear superposition imply that two sound waves, passing through the same place at the same time, always create a louder sound than either wave alone? Explain.

3. Can two light beams ever cancel each other out and result in darkness? Explain.

4. Two pulses are traveling toward each other, each having a speed of 1 cm/s. At t = 0 s, their positions are shown in the drawing. When t = 1 s, what is the height of the resultant pulse at

a. x = 3 cm

b. x = 4 cm

5. What is the primary difference between mechanical waves and electromagnetic waves?

6. What is the amplitude of a wave and what does it represent?

7. What is the difference between transverse and longitudinal waves?

8. You are creating transverse waves in a rope by shaking your hand from side to side. Without changing the distance that your hand moves, you begin to shake it faster and faster. What happens to the amplitude, wavelength, frequency, period, and speed of the wave?

9. How could you demonstrate that a transverse wave transports energy without transferring matter?

10. Describe longitudinal waves. What types of media transmit longitudinal waves? Compare the speed through each.

11. AM radio signals are broadcast at frequencies between 550 kHz and 1600 kHz. What is the range of wavelengths for these signals?

12. FM frequencies range between 88 MHz and 108 MHz. What is the range of wavelengths for these signals?

13. After seeing lightning flash, it takes 3 s for you to hear the thunder. Both waves travel the same distance and were created simultaneously. How far away is the storm? Assume sound travels at 343 m/s.

14. What is the energy of a photon of yellow-green light with a frequency of 5.5 x 1014 Hz?

15. Blue light has a frequency of 6.34 x 1014 Hz. What is the energy of a photon of blue light?

16. If a person could travel at the speed of light, it would still take 4.3 years to reach the nearest start, Proxima Centauri. How far away is Proxima Centauri?

17. What is the energy of a photon of blue light with a wavelength of 450 nm?

18. What is the energy of a photon of red light with a wavelength of 700 nm?

19. Which colored light bulb – red, orange, yellow, green, or blue – emits photons with the least and most energy? Explain.

20. Ultraviolet light is responsible for sun tanning. Find the wavelength of an ultraviolet photon whose energy is 5.4 x 10-19 J.

21. What is the speed of light in benzene that has an index of refraction of 1.501?

22. Light has a wavelength of 340 nm and a frequency of 5.403 x 1014 Hz when traveling trough a certain substance. What is the index of refraction for this substance?

23. You notice that when a light ray enters a certain liquid from water, it is bent toward the normal, but when it enters the same liquid from crown glass, it is bent away from the normal. What can you conclude about the liquid’s index of refraction?

24. A ray of light in air has an angle of incidence of 30˚ on a block of unknown material and an angle of refraction of 20˚. What is the index of refraction of the material?

25. Could an index of refraction ever be less than 1? What would this imply about the speed of light in the medium?

26. What is the speed of light in chloroform with n = 1.51?

27. A beam of light passes from water (n = 1.33) into polyethylene with n = 1.5. If the angle of incidence is 57.5˚, what is the angle of refraction in the polyethylene?

28. A sign painted on a store window is reversed when viewed from inside the store. If a person inside the store views the reversed sign in a plane mirror, does the sign appear as it would when viewed from outside the store? (Try it by writing some letters on a transparent sheet of paper and then holding the back side of the paper up to a mirror.) Explain.

29. If a clock is held in front of a mirror, its image is reversed left to right. From the point of view of a person looking into the mirror, does the image of the second hand rotate in the reverse (counter-clockwise) direction? Justify your answer.

30. If you are standing 2 m in front of a flat mirror, how far behind the mirror is your image? What is the magnification of the image?

31. Two flat mirrors make an angle of 90˚ with each other. An incoming ray makes an angle of 35˚ with the normal of the first mirror. Determine the angle of reflection off of the second mirror.

32. Marian admires a new dress in a department store dressing room mirror. If Marian stands as shown, making an angle of 70˚ with the center mirror, at what angle will the light be reflected from the mirror on the right?

33. Your friend is stranded 10 m high in a tall tree with a hungry tiger beneath, while you lie on the beach a distance away. He has only a mirror, which he uses to signal you by holding it perpendicularly to the horizon as shown. If the sun hits the mirror at a 30˚ angle to the normal and reflects back in your eye, how fat away are you from the base of the tree?

34. In order to see your back teeth more easily, your dentist uses a small mirrored instrument that can be easily manipulated in your mouth. If the dentist places this mirror directly under a rear molar, and tilts it 20˚, at what angle to the normal will the dentist need to look into the mirror in order to see the tooth?

35. You want to start a fire with a spherical mirror.a. Which kind of spherical mirror, concave or convex, can be used to start the fire with sunlight? Explain.

b. For the best results, how far from the mirror should the paper to be ignited be placed? Explain.

36. Can the image formed by a concave mirror ever be projected directly onto a screen, without the help of other mirrors or lenses? If so, specify where the object should be placed relative to the mirror.

37. Can the image formed by a convex mirror ever be projected directly onto a screen, without the help of other mirrors or lenses? If so, specify where the object should be placed relative to the mirror.

38. Why, when you look at the back side of a shiny teaspoon, held at arm’s length, you see yourself upright? Why do you see yourself upside down when you look a the other side of the spoon?

39. Sometimes news personnel covering an event use a microphone arrangement that is designed to increase the ability of the mike to pick up weak sounds. The drawing shows that the arrangement consists of a hollowed-out shell behind the mike. The shell acts like a mirror for sound waves. Explain how this arrangement enables the mike to detect weak sounds.

40. Suppose you stand in front of a spherical mirror (concave or convex). a. Is it possible for your image to be real and upright? Explain.

b. Is it possible for your image to be virtual and inverted? Explain.