Exam IV: Chapters 20 24

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1 PHYS 1420: College Physics II Fall 2008 Exam IV: Chapters We want to use the magnet shown on the let to induce a current in the closed loop o wire. s shown in the picture, your eye is at some position +x, and you are looking at the loop in the yz-plane. The magnet is pushed toward you, in the +x direction. 1. The direction o the current in the loop is ) clockwise. B) counterclockwise. C) neither; no current is induced. 2. I we keep the magnet stationary, and spin the loop clockwise (loop is initially in the yz-plane, spin with respect to y-axis), ) the magnetic lux through the loop decreases until the loop is lat (in the xy-plane o the paper). B) the magnetic lux increases until the loop is lat. C) the magnetic lux does not change. It is zero no matter how you spin the loop o wire. D) the magnetic lux remains constant (and non zero)because the magnetic ield remains constant. E) the lux changes, but there is no way to tell i it is increasing or decreasing unless we have the area o the loop and the number o coils that make up the loop. 3. True or alse: Gamma rays have about double the requency o microwave radiation. 4. True or alse: Radio waves with a wavelength o 1m travel 10 times aster through space than x rays with a wavelength o m. 5. What is the requency o red light which has a wavelength o 750nm (7.5x10 7 m)? ) = 7.5x10 14 Hz. B) = 2.5x10 14 Hz. C) = 4x10 14 Hz. D) = 5x10 14 Hz. E) = 7.5x10 14 Hz. 6. True or alse: Ultraviolet radiation with requency Hz is literally 1000 times more energetic than inrared radiation with a requency o Hz. 7. Compute the energy o visible light having a wavelength λ = 7x10 7 m. Planck s constant h = 6.63x10 34 J s. ) 4.6x10 40 J. B) 2.8x10 19 J. C) 46.4J. D) 3.6x10 18 J. E) 7.5x10 43 J. 8. The law o relection states that ) incoming light is relected back along its original path. B) the angle o incidence is equal to the angle o relection. C) the angles o incidence and relection always add up to 90. D) or curved mirrors, the angle o relection is twice the angle o incidence. E) angle o incidence only equals angle o relection or lat, perectly smooth, plane mirrors. 9. Diuse relection occurs when ) randomly oriented rays o light are passed through a narrow aperture. The result is a narrow beam o polarized light. B) randomly oriented rays o incoming light relect o a smooth surace. The relected rays are all normal to the surace. C) randomly oriented rays o incoming light relect o a rough surace. The relected rays are all normal to the surace. D) parallel rays o light are relected rom a rough or uneven surace. The relected rays are not parallel. E) parallel rays o incoming light are relected rom a smooth surace. The relected rays are parallel.

2 10. The principle o least time states that ) the shortest distance between two points is a straight line. B) the shortest path between two points is always the astest path. C) a beam o light will always ollow the astest path rom one point to another. D) a beam o light will always travel along the shortest path rom one point to another. E) it always takes less time or light to travel a path than anything else. 11. When light passes rom one medium to another, ) it changes speed. The wave will change direction, bending toward the slower medium. B) it continues to travel at 3x10 8 m/s regardless o the type o medium or the angle o incidence. C) it always slows down, and it always reracts by the same amount regardless o the angle o incidence. D) it always speeds up, and it never reracts unless the angle o incidence is less than the critical angle. E) it bends only when it strikes the boundary between the media at a 90 angle to the surace. beam o light is shown on the right striking a boundary between two media. Neither medium is vacuum or air, and Medium 1 is not the same as Medium 2. nswer questions 12 through 14 using this ray diagram. 12. t what angle o incidence will the incident ray experience no reraction as it crosses the boundary into Medium 2? ) When θ1 = 90, θ2 = 0. B) When θ1 = 45, θ2 = 45. This is zero reraction. C) When θ1 = zero, θ2 also = 0. D) There is no possible incident angle or zero reraction, since the two media are not the same. 13. True or alse: The index o reraction n1 must be greater than the index o reraction n True or alse: There exists a critical angle o incidence θc beyond which any incident light will be totally internally relected back into Medium The index o reraction or water is n = What is the speed o light through this medium? ) v = 1.6x10 8 m/s. B) v = 1.9x10 8 m/s. C) v = 2.3x10 8 m/s. D) v = 3x10 8 m/s. 16. Light traveling through air strikes the plastic surace o a transparent tabletop at an angle o 20 with respect to the normal. The index o reraction or lucite is n = Find the angle o reraction. ) θ=13.2 B) θ=25.5 C) θ=41.0 D) θ=73.9 E) θ= What is the critical angle or total internal relection or lucite (n=1.495) and air (n=1)? ) θ = 0 B) θ = 42 C) θ = 44 D) θ = 46 E) θ = You are driving I-40 across New Mexico. It's gorgeous! Suddenly your sister wakes up and yells, "Watch out! The road is wet! Don't skid!" What do you do? ) Remind her o that time when you were little and she thought that i you ate Pop Rocks while drinking a Coke your head would explode. Then make un o her hair rom sleeping in the car. B) Slow down and pull over. The road really is wet, and since you're in New Mexico on a sunny day, it's probably a trap. When you spin out on the wet road the aliens come and abduct you. C) The road probably is wet, but there are no aliens. The water condenses on the highway because it is warmer than the surrounding desert. Just drive careully, but you don't need to panic. D) Nothing. Well, keep right on singing really loud along with the radio, but you don't need to worry about the road. It's a mirage caused by the reraction o light through the air. E) Keep singing, but know that the mirage is not a result o reraction at all. It is a dispersion eect, as red light and blue light are relected dierently o the surace o the highway. screen White light shines through a prism and strikes a screen as shown on the let. 19. In what order do the colors appear on the screen? ) ROY G BIV, reading rom top to bottom. B) ROY G BIV, reading rom bottom to top. C) BRIG V OY, reading rom bottom to top. D) GIB V YOR, reading rom top to bottom. E) The colors might appear in any order at all. It depends on the index o reraction o the glass used to make the prism. Page 02

3 20. Incoming light strikes the mirror M1 as shown on the right. t what angle with respect to the normal to mirror M2 will the relected ray inally emerge? Notice that M2 is not perpendicular to M1! Remember also that the angles o any triangle must add up to 180. Enter the numeric answer or the relection angle True or alse: To increase the ield o view o a plane mirror, just hold it arther away rom you. Double the distance, double the ield o view. 22. You are at the Target store buying some great new stu to redecorate your room! Plus, you can always use some sock monkey pajamas, ziploc bags, candy, wine glasses, cereal, and a ew DVDs. It s the holidays! Shop on! I you are precisely 6 eet tall, how long should the 120 mirror you plan to buy be i you want to use it as a ull-length mirror? ) ny size will work. The arther away you get, the more o yoursel you will see. B) The mirror must be at least 6 eet long, or you will never see your complete image. C) The mirror must be exactly 3 t tall, i you stand exactly 6 eet away rom it. I you move any closer to the mirror, it needs to be bigger or you to see your complete image. D) The ratio o mirror height to object distance must be exactly ½. This means that i you have a mirror 1t tall, you must stand 2t away rom it to see your entire image. Your height does not matter. E) The mirror must be at least hal your height, and your distance rom the mirror is not material. 23. When you use a second mirror to look at the back o your head, you are seeing ) the real image o a real object. C) the virtual image o a real object. B) the real image o a virtual object. D) the virtual image o a virtual object. 24. person stands 2 m in ront o a plane mirror and lexes his imaginary biceps. His image ) is virtual, located 2 m in ront o the mirror. B) is virtual, located exactly at the surace o the mirror. C) is virtual, located 2 m behind the mirror. D) is real, located 2 m in ront o the mirror. E) is real, located 2 m behind the mirror. 25. Now he is holding a hairbrush and singing into it like it s a microphone (maybe we should leave beore he starts combing over his bald spot). The brush is 20 cm tall. The image o the brush is ) inverted and miniied. The image will appear smaller than the object, and the arther away he stands, the smaller the image. B) inverted and magniied. The image height depends on how ar rom the mirror he stands, but it will be greater than 20 cm.. C) upright and magniied. The image height depends on how ar rom the mirror he stands, but it will be greater than 20 cm. D) upright and unmagniied. Unless the mirror is curved, it cannot orm any image that is bigger (or smaller) than the actual object. E) upright and miniied. The image will appear smaller than the object, and the arther away he stands, the smaller the image. B C D concave mirror is placed as shown on the let. The light source is to the let o the mirror, and you are going to place a real object. nswer questions 26 and 27 using the letters on the picture or your responses through D. I you think that the correct response is T or F, use the TRUE or FLSE keys on your responder. 26. In order to orm an image that is inverted, where should you E) Either region or B will create an inverted relection. F) Nowhere! concave mirror cannot invert an image. T) nywhere! concave mirror can only orm real images. 27. In order to orm an image that is magniied, where should you E) Either region B or C will create a magniied F) Nowhere! concave mirror cannot magniy. image. T) nywhere! concave mirror only orms magniied images. Page 03

4 convex mirror is placed as shown on the right. The light source is to the let o the mirror, and you are going to place a real object. nswer questions 28 and 29 using the letters on the picture or your responses through D. I you think that the correct response is T or F, use the TRUE or FLSE keys on your responder. 28. In order to orm an image that is inverted, where should you E) ny region, B, C, or D will create an inverted relection. F) nywhere! convex mirror can only orm real images. T) Nowhere! convex mirror cannot invert an image. 29. In order to orm an image that is magniied, where should you E) Either region C or D will create a magniied image. F) nywhere! convex mirror can only magniy images. T) Nowhere! convex mirror cannot magniy an image. 2 B C D E) Either region B or C will create a magniied image. convex lens is placed as shown on the let. The light source is to the let o the lens, and you are going to place a real object. nswer questions 30 and 31 using the letters on the picture or your responses through D. I you think that the correct response is T or F, use the TRUE or FLSE keys on your responder. 30. In order to orm a real image, where should you place an object? E) Either region or B will create a real image. F) Either region B or C will create a real image. T) Nowhere! convex lens cannot orm a real image. 31. In order to orm an image that is magniied, where should you F) nywhere! convex lens can only magniy images. T) Nowhere! convex lens cannot magniy an image. 32. True or alse: n object placed precisely at do = 2 will orm an image that has a magniication M = True or alse: n object placed precisely at do = will orm an image that has a magniication M = The converging lens above has a ocal length = 15cm. Locate the image (di) ormed when an object (ho = 2cm) is placed at a distance do = 10cm. nswer with two sig igs, and include sign where appropriate. di = 30 cm 35. The image ormed in question 34 is ) real, inverted, magniied. B) real, inverted, miniied. C) real, upright, unmagniied. concave lens is placed as shown on the let. The light source is to the let o the lens, and you are going to place a real object. nswer questions 36 and 37 using the letters on the picture or your responses through D. I you think that the correct response is T or F, use the TRUE or FLSE keys on your responder. 36. In order to orm a virtual image, where should you position an object? E) Either region or B will create a virtual image. F) Nowhere! concave lens cannot orm virtual images. T) nywhere! concave lens can only create virtual images. D) virtual, upright, magniied. E) virtual, upright, miniied. B C D 37. In order to orm an image that is magniied, where should you E) Either region B or C will create a magniied image. T) Nowhere! concave lens cannot magniy an F) nywhere! concave lens can only magniy images. image. 38. True or alse: n object placed precisely at do = 2 will orm an image that has a magniication M = diverging lens has a ocal length = 15cm. When an object is placed at do = 10cm, where does the image orm? nswer with two sig igs, and include sign. di = 6 cm 40. What is the magniication o the image ormed in question 39? nswer with two sig igs, and include sign. M = B C D Page 04

5 1 = 15 cm 2 = 10 cm x = 40 cm do = 40 cm do ) d = 6cm, placing it 6 cm to the let o the concave lens. B) d = +6cm, placing it 6 cm to the right o the concave lens. C) d = +7cm, placing it 7 cm to the right o the concave lens. D) d = 7cm, placing it 7 cm to the let o the concave lens. x The compound lens system shown on the let consists o a converging lens with ocal length 1 = 15 cm, and a diverging lens with a ocal length 2 = 10 cm. The lenses are separated by a distance x = 40 cm, and a real object is positioned to the let o the convex lens, at a distance do = 40 cm. The convex lens will orm the irst image, which will be located 24cm to the right o the irst lens. This image becomes the object or the diverging lens, which orms the inal image. 41. Locate the position o the inal image. E) There is no inal image ormed, because the irst image is to the right o the second lens. You cannot orm an image o a virtual object! 42. Describe the inal image o the arrow. ) The inal image arrow is upside down and smaller than the original object. B) The inal image arrow is right-side up, and smaller than the original object. C) The inal image arrow is upside down and larger than the original arrow. D) The inal image arrow is right-side up and larger than the original arrow. E) The inal image arrow is exactly the same size as the object, and points in the same direction as well. 43. Young's double slit experiment ) demonstrates convincingly that light is a particle. The pattern created on a screen shows two bright ringes that line up exactly with the position o each slit. There is a dark ringe on center, which you would expect since no particle passing through a slit could actually hit the center o the screen. B) demonstrates conclusively that light is a wave. The alternating pattern o bright and dark ringes on the screen show how two light waves interere. The central bright maximum proves that the light can't be a particle. C) proves that light is a particle. When a bright light shines on a metal oil, the photons crash into the surace and knock electrons right o. Young observed that a wave could not do this, but he could not explain why. Einstein actually explained it, and won a Nobel Prize or his mathematical proo o Young's hypothesis. D) showed that light has a dual wave particle nature. Newton irst suggested this, but got distracted by trying to turn lead into gold beore he could prove it. Young's experiment laid the groundwork or Maxwell, whose equations inally proved that electricity is a wave and magnetism is a particle. Page 05