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The spaceship at S wishes to touch the surface of the giant planet and proceed to point X in the shortest distance possible. To what point P on the planet surface should the spaceship travel? Ch 28-1 1. Point a 2. Point b 3. Point c 4. Actually, all yield the same total distance.

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The spaceship at S wishes to touch the surface of the giant planet and proceed to point X in the shortest distance possible. To what point P on the planet surface should the spaceship travel? Ch 28-1 Answer: 2 The spaceship should first travel to Point b. Create a reflection of S below the planet surface and call it S. Then the distance SPX equals S PX, which will be the shortest when S PX is a straight line. Can you see that P is the point wherein SP and PX make the same angle with the ground? 1. Point a 2. Point b 3. Point c 4. Actually, all yield the same total distance.

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In order that you are able to see a full-length view of yourself, the minimum size for a plane mirror must be 1. one-quarter your height. 2. one-half your height. 3. three-quarters your height. 4. your full height. 5. … depends on your distance. Ch 28-2

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In order that you are able to see a full-length view of yourself, the minimum size for a plane mirror must be 1. one-quarter your height. 2. one-half your height. 3. three-quarters your height. 4. your full height. 5. … depends on your distance. Ch 28-2 Answer: 2 Consistent with the law of reflection. If you look halfway down a plane mirror in front of you, you’ll see your toes. If you look at parts of the mirror below the halfway mark, you’ll see the floor but not yourself. If you look straight ahead, you’ll see your eyes. If you look above at a distance halfway from your eyes to the top of your head, you’ll see the top of your head. You don’t see your image in parts of the mirror above. Halfway up; halfway down—that’s a mirror one-half your height. As the sketch below shows, distance is not a factor.

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**To see more of her head in the mirror, she**

Ch 28-4 1. should hold the mirror closer. 2. should hold the mirror farther away. 3. needs a bigger mirror.

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**To see more of her head in the mirror, she **

Answer: 3 If she holds the mirror closer, her image appears bigger, but so does the mirror. If she holds the mirror farther away, both her image and the mirror are proportionally reduced. As the ray diagrams show, she sees the same proportion of her face at any distance. Try this yourself and see! And if you cannot see your full face, you need a bigger mirror. How big? At least half the size of your face. Ch 28-4 1. should hold the mirror closer. 2. should hold the mirror farther away. 3. needs a bigger mirror.

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1. 2. She takes a photograph of her friend standing on the bridge as shown. Which of the two sketches more accurately shows the photograph of the bridge and its reflection? Ch 28-5

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1. 2. She takes a photograph of her friend standing on the bridge as shown. Which of the two sketches more accurately shows the photograph of the bridge and its reflection? Ch 28-5 Answer: 2 The second sketch shows a more accurate reflection of the bridge. The reflected view is not simply an inversion of the scene above, as some people think, but is the scene as viewed from a lower position—from below the water surface. The reflected view of the bridge is the view the girl would see if her head were as far below the water surface as her eye is above it. Hence the reflected view shows the underside of the bridge.

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Light rays bend as they pass from air into water at a non–90 degree angle. This is refraction. Which quantity doesn’t change when light refracts? 1. Average speed of light 2. Material’s index of refraction 3. Frequency of light 4. Wavelength of light Ch 28-7 Thanks to Don Kanner.

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Light rays bend as they pass from air into water at a non–90 degree angle. This is refraction. Which quantity doesn’t change when light refracts? 1. Average speed of light 2. Material’s index of refraction 3. Frequency of light 4. Wavelength of light Ch 28-7 Thanks to Don Kanner. Answer: 3 The average speed of light in water is less than in air. Index of refraction is a quantity that changes when wave speed changes (higher index for lower speed). So we see the index of refraction is greater for water than for air. The wave just outside the surface “drives” the wave just inside the surface, so their rates of vibration match. Hence, what doesn't change is frequency. Same frequency and reduced speed means a shorter wavelength in water—as seen by the “compressed” wave fronts in the sketch.

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**1. above 2. below 3. directly at the observed fish.**

Jose wishes to “spear” a fish with a laser. In order to make a direct hit, he should aim the laser beam Ch 28-8 1. above 2. below 3. directly at the observed fish.

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**1. above 2. below 3. directly at the observed fish.**

Jose wishes to “spear” a fish with a laser. In order to make a direct hit, he should aim the laser beam Ch 28-8 Answer: 3 Jose should aim directly at the fish he sees. If he were instead throwing a spear, he’d have to compensate for the refraction of light and aim below the observed fish. But not if the “spear” is a light beam! A light path is reversible, and will go from A to B along the same path it takes from B to A. 1. above 2. below 3. directly at the observed fish.

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Suppose you want to send a beam of laser light to a space station above the atmosphere and just above the horizon. You should aim your laser Ch 28-9 1. slightly higher than 2. slightly lower than 3. directly along the line of sight to the space station.

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Suppose you want to send a beam of laser light to a space station above the atmosphere and just above the horizon. You should aim your laser Ch 28-9 Answer: 3 To send light to the space station, make no corrections and simply aim at the station you see. All deviations due to atmospheric refraction in your line of sight will be the same for your laser beam—principle of reciprocity. 1. slightly higher than 2. slightly lower than 3. directly along the line of sight to the space station.

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**1. nearsighted. 2. farsighted. 3. neither.**

A person who sees more clearly under water than in air without eyeglasses is Ch 28-10 1. nearsighted. 2. farsighted. 3. neither.

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**1. nearsighted. 2. farsighted. 3. neither.**

A person who sees more clearly under water than in air without eyeglasses is Ch 28-10 Answer: 1 The speed of light in water is less than in air, so the change in speed is less as light goes from water to your eye. Less refraction occurs. This makes all people more farsighted under water, which is advantageous if you’re nearsighted. If you’re very nearsighted, the image may fall on your retina and you’ll see as clearly under water as a person with normal vision who wears an air-enclosed mask. 1. nearsighted. 2. farsighted. 3. neither.

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The photographer wishes to photograph the rainbow but is disappointed to find the camera’s angle of view is not wide enough to see the whole rainbow. To get the whole rainbow, she would be better off if she were 1. closer to the rainbow. 2. farther from the rainbow. 3. … neither, for she’d get the same portion of rainbow in either case. Ch 28-13

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The photographer wishes to photograph the rainbow but is disappointed to find the camera’s angle of view is not wide enough to see the whole rainbow. To get the whole rainbow, she would be better off if she were 1. closer to the rainbow. 2. farther from the rainbow. 3. … neither, for she’d get the same portion of rainbow in either case. Ch 28-13 Answer: 3 Any full circle rainbow, near or far, subtends an angle of 84°. So to photograph a full rainbow, whether a very close one produced by a hand-held garden hose or one miles away, the camera’s field of view must be at least 84°—a very wide-angle lens. It is the angle of view, not the distance, that matters.

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ConcepTest 23.1 Reflection

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