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© 2005 Pearson Prentice Hall This work is protected by United States copyright laws and is provided solely for the use of instructors in teaching their courses and assessing student learning. Dissemination or sale of any part of this work (including on the World Wide Web) will destroy the integrity of the work and is not permitted. The work and materials from it should never be made available to students except by instructors using the accompanying text in their classes. All recipients of this work are expected to abide by these restrictions and to honor the intended pedagogical purposes and the needs of other instructors who rely on these materials. ConcepTest PowerPoints Chapter 23 Physics: Principles with Applications, 6 th edition Giancoli

ConcepTest 23.1Reflection When watching the Moon over the ocean, you often see a long streak of light on the surface of the water. This occurs because: 1) the Moon is very large 2) atmospheric conditions are just right 3) the ocean is calm 4) the ocean is wavy 5) motion of the Moon

angle of incidence also changesdifferent spots on the water can reflect the Mooninto your eyes at different times When the water surface changes, the angle of incidence also changes. Thus, different spots on the water can reflect the Moon into your eyes at different times. ConcepTest 23.1Reflection When watching the Moon over the ocean, you often see a long streak of light on the surface of the water. This occurs because: 1) the Moon is very large 2) atmospheric conditions are just right 3) the ocean is calm 4) the ocean is wavy 5) motion of the Moon Follow-up: Where else does this occur?

ConcepTest 23.2aMirror I S O 1 2 3 4 mirror An observer at point O is facing a mirror and observes a light source S. Where does the observer perceive the mirror image of the source to be located?

ConcepTest 23.2aMirror I S O 1 2 3 4 mirror Trace the light rays from the object to the mirror to the eye. Since the brain assumes that light travels in a straight line, simply extend the rays back behind the mirror to locate the image. An observer at point O is facing a mirror and observes a light source S. Where does the observer perceive the mirror image of the source to be located? Follow-up: What happens when the observer starts moving toward the mirror? toward the mirror?

ConcepTest 23.2bMirror II You stand in front of a mirror. How tall does the mirror have to be so that you can see yourself entirely? 1) same as your height 2) less than your full height but more than half your height 3) half your height 4) less than half your height 5) any size will do

ConcepTest 23.2bMirror II  i =  r mirror only half your size Trace the light rays from the image’s foot to the mirror and then to the eye. Since we know that  i =  r, you need a mirror only half your size. You stand in front of a mirror. How tall does the mirror have to be so that you can see yourself entirely? 1) same as your height 2) less than your full height but more than half your height 3) half your height 4) less than half your height 5) any size will do

ConcepTest 23.2cMirror III Does this depend on your distance from the mirror? 1) No. 2) Yes. 3) Depends on the mirror. 4) Depends on the person.

ConcepTest 23.2cMirror III Does this depend on your distance from the mirror? 1) No. 2) Yes. 3) Depends on the mirror. 4) Depends on the person. The further you step back, the smaller the incident and reflected angles will be. But the rays will still be reflected at the same points, so the ray from the foot will still be reflected at mid- height.

ConcepTest 23.3All Smoke and Mirrors 1.0 m 0.5 m 1) 0.5 m 2) 1.0 m 3) 1.5 m 4) 2.0 m 5) 2.5 m You hold a hand mirror 0.5 m in front of you and look at your reflection in a full-length mirror 1 m behind you. How far in back of the big mirror do you see the image of your face?

small mirror0.5 m big mirror2.0 m 2.0 mbig mirror The image of the face reflected in the small mirror appears 0.5 m behind the small mirror. This image (which is the object for the big mirror) is 2.0 m away from the big mirror. The final image is 2.0 m behind the big mirror. ConcepTest 23.3All Smoke and Mirrors 1.0 m 0.5 m 1) 0.5 m 2) 1.0 m 3) 1.5 m 4) 2.0 m 5) 2.5 m You hold a hand mirror 0.5 m in front of you and look at your reflection in a full-length mirror 1 m behind you. How far in back of the big mirror do you see the image of your face?

ConcepTest 23.4aRefraction I 1 air Parallel light rays cross interfaces from air into two different media, 1 and 2, as shown in the figures below. In which of the media is the light traveling faster? 1) medium 1 2) medium 2 3) both the same 2

ConcepTest 23.4aRefraction I 1 air The greater the difference in the speed of light between the two media, the greater the bending of the light rays. Parallel light rays cross interfaces from air into two different media, 1 and 2, as shown in the figures below. In which of the media is the light traveling faster? 1) medium 1 2) medium 2 3) both the same 2 Follow-up: air 12? Follow-up: How does the speed in air compare to that in 1 or 2?

ConcepTest 23.4bRefraction II 1 3 2 Parallel light rays cross interfaces from medium 1 into medium 2 and then into medium 3. What can we say about the relative sizes of the index of refraction of these media? 1) n 1 > n 2 > n 3 2) n 3 > n 2 > n 1 3) n 2 > n 3 > n 1 4) n 1 > n 3 > n 2 5) none of the above

ConcepTest 23.4bRefraction II bent toward the normal n 2 > n 1 bent away from the normaln 3 n 1 > n 3 The rays are bent toward the normal when crossing into #2, so n 2 > n 1. But rays are bent away from the normal when going into #3, so n 3 n 1 > n 3. 1 3 2 Parallel light rays cross interfaces from medium 1 into medium 2 and then into medium 3. What can we say about the relative sizes of the index of refraction of these media? 1) n 1 > n 2 > n 3 2) n 3 > n 2 > n 1 3) n 2 > n 3 > n 1 4) n 1 > n 3 > n 2 5) none of the above

ConcepTest 23.5aGone Fishin’ I To shoot a fish with a gun, should you aim directly at the image, slightly above, or slightly below? 1) aim directly at the image 2) aim slightly above 3) aim slightly below

ConcepTest 23.5aGone Fishin’ I higher aimlower Due to refraction, the image will appear higher than the actual fish, so you have to aim lower to compensate. To shoot a fish with a gun, should you aim directly at the image, slightly above, or slightly below? 1) aim directly at the image 2) aim slightly above 3) aim slightly below

ConcepTest 23.5bGone Fishin’ II 1) aim directly at the image 2) aim slightly above 3) aim slightly below To shoot a fish with a laser gun, should you aim directly at the image, slightly above, or slightly below?

light bend aim directly at the fish The light from the laser beam will also bend when it hits the air-water interface, so aim directly at the fish. ConcepTest 23.5bGone Fishin’ II laser beam light from fish 1) aim directly at the image 2) aim slightly above 3) aim slightly below To shoot a fish with a laser gun, should you aim directly at the image, slightly above, or slightly below?

ConcepTest 23.6Parallel Lines An observer views two closely spaced lines through an angled piece of glass. To the observer, the lines appear: 1) shifted to the right 2) shifted to the left 3) spaced farther apart 4) spaced closer together 5) no change – same as before

shift to the left The light rays get refracted twice, so they remain parallel, but they shift to the left, as seen in the figure. Their relative spacing does not change, just the overall position. ConcepTest 23.6Parallel Lines An observer views two closely spaced lines through an angled piece of glass. To the observer, the lines appear: 1) shifted to the right 2) shifted to the left 3) spaced farther apart 4) spaced closer together 5) no change – same as before Follow-up: Follow-up: What happens when the top glass moves toward the bottom glass?

ConcepTest 24.1Superposition 1) 2) 3) 4) If waves A and B are superposed (that is, their amplitudes are added) the resultant wave is

The amplitudes of waves A and B have to be added at each point! ConcepTest 24.1Superposition 1) 2) 3) 4) If waves A and B are superposed (that is, their amplitudes are added) the resultant wave is

ConcepTest 24.2aPhase Difference I The two waves shown are 1) out of phase by 180 o 2) out of phase by 90 o 3) out of phase by 45 o 4) out of phase by 360 o 5) in phase

1/4 wavelength 90 o The two waves are out of phase by 1/4 wavelength (as seen in the figure), which corresponds to a phase difference of 90 o. ConcepTest 24.2aPhase Difference I 1/4 The two waves shown are 1) out of phase by 180 o 2) out of phase by 90 o 3) out of phase by 45 o 4) out of phase by 360 o 5) in phase Follow-up: Follow-up: What would the waves look like for no. 4 to be correct?

ConcepTest 24.2bPhase Difference II 1) out of phase by 180 o 2) out of phase, but not by 180 o 3) in phase Two light sources emit waves of = 1 m which are in phase. The two waves from these sources meet at a distant point. Wave 1 traveled 2 m to reach the point, and wave 2 traveled 3 m. When the waves meet, they are

twice this wavelengththree times this wavelength one full wavelength, Since = 1 m, wave 1 has traveled twice this wavelength while wave 2 has traveled three times this wavelength. Thus, their phase difference is one full wavelength, which means they are still in phase. ConcepTest 24.2bPhase Difference II 1) out of phase by 180 o 2) out of phase, but not by 180 o 3) in phase Two light sources emit waves of = 1 m which are in phase. The two waves from these sources meet at a distant point. Wave 1 traveled 2 m to reach the point, and wave 2 traveled 3 m. When the waves meet, they are

ConcepTest 24.3aDouble Slits I 1) spreads out 2) stays the same 3) shrinks together 4) disappears In a double-slit experiment, when the wavelength of the light is increased, the interference pattern

is increasedd does not change  must increase If is increased and d does not change, then  must increase, so the pattern spreads out. ConcepTest 24.3aDouble Slits I 1) spreads out 2) stays the same 3) shrinks together 4) disappears d sin  = m  d sin  = m  In a double-slit experiment, when the wavelength of the light is increased, the interference pattern

ConcepTest 24.3b Double Slits II 1) spreads out 2) stays the same 3) shrinks together 4) disappears If instead the slits are moved farther apart (without changing the wavelength) the interference pattern

If instead d is increased and does not change, then  must decrease, so the pattern shrinks together ConcepTest 24.3b Double Slits II 1) spreads out 2) stays the same 3) shrinks together 4) disappears d sin  = m  If instead the slits are moved farther apart (without changing the wavelength) the interference pattern Follow-up: Follow-up: When would the interference pattern disappear?

1) there is no difference 2) half a wavelength 3) one wavelength 4) three wavelengths 5) more than three wavelengths In a double-slit experiment, what path difference have the waves from each slit traveled to give a minimum at the indicated position? Intensity ConcepTest 24.4Path Difference

Intensity 7 /2 /2 3 /2 5 /2 For Destructive Interference  = 1/2, 3/2, 5/2, 7/2, … = (m + 1/2) 2 3 1) there is no difference 2) half a wavelength 3) one wavelength 4) three wavelengths 5) more than three wavelengths In a double-slit experiment, what path difference have the waves from each slit traveled to give a minimum at the indicated position? ConcepTest 24.4Path Difference

1) pattern vanishes 2) pattern expands 3) bright and dark spots are interchanged 4) pattern shrinks 5) no change at all An interference pattern is seen from two slits. Now cover one slit with glass, introducing a phase difference of 180° (1/2 wavelength) at the slits. How is the pattern altered? Double slit Interference pattern wave ConcepTest 24.5Interference Pattern

phase difference of 180° dark bright and dark spots are interchanged If the waves originating from the two slits have a phase difference of 180° when they start off, the central spot will now be dark !! To the left and the right, there will be bright spots. Thus, bright and dark spots are interchanged. Double slit Interference pattern wave 1) pattern vanishes 2) pattern expands 3) bright and dark spots are interchanged 4) pattern shrinks 5) no change at all An interference pattern is seen from two slits. Now cover one slit with glass, introducing a phase difference of 180° (1/2 wavelength) at the slits. How is the pattern altered? ConcepTest 24.5Interference Pattern Follow-up: ° Follow-up: What happens when the phase difference is 90°?

ConcepTest 24.5aDiffraction I The diffraction pattern below arises from a single slit. If we would like to sharpen the pattern, i.e., make the central bright spot narrower, what should we do to the slit width? 1) narrow the slit 2) widen the slit 3) enlarge the screen 4) close off the slit

The angle at which one finds the first minimum is: The central bright spot can be narrowed by having a smaller angle. This in turn is accomplished by widening the slit. ConcepTest 24.5aDiffraction I d    sin  =  d The diffraction pattern below arises from a single slit. If we would like to sharpen the pattern, i.e., make the central bright spot narrower, what should we do to the slit width? 1) narrow the slit 2) widen the slit 3) enlarge the screen 4) close off the slit

ConcepTest 24.5bDiffraction II Blue light of wavelength passes through a single slit of width d and forms a diffraction pattern on a screen. If the blue light is replaced by red light of wavelength 2, the original diffraction pattern can be reproduced if the slit width is changed to: 1) d/4 2) d/2 3) no change needed 4) 2 d 5) 4 d

ConcepTest 24.5bDiffraction II d    d sin  = m (minima)  2 d  2dfor sin  to remain unchanged If  2 then we must have d  2d for sin  to remain unchanged (and thus give the same diffraction pattern). Blue light of wavelength passes through a single slit of width d and forms a diffraction pattern on a screen. If the blue light is replaced by red light of wavelength 2, the original diffraction pattern can be reproduced if the slit width is changed to: 1) d/4 2) d/2 3) no change needed 4) 2 d 5) 4 d

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