AP Physics 2 Quiz: Diffraction

What this quiz covers

This quiz focuses on Diffraction, giving you a quick way to practice the rules, question types, and explanations that matter most for AP Physics 2.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

Question 1

1. Setup 1, because the wavelength is larger relative to the slit width (correct answer)
2. Setup 2, because the wavelength is smaller relative to the slit width
3. Setup 1, because the amplitude is the same so diffraction increases
4. Setup 2, because the wave speed is higher for shorter wavelengths

Explanation: This question tests understanding of diffraction. Diffraction is the spreading of waves through openings, with the amount of spreading depending on the ratio of wavelength to opening size. Setup 1, with longer wavelength waves passing through the same slit width, will show greater diffraction because the wavelength is larger relative to the slit width. The diffraction angle is proportional to λ/a, where λ is wavelength and a is slit width, so larger wavelengths produce more spreading. Choice B represents the misconception that smaller wavelengths diffract more, but actually smaller wavelengths relative to the opening result in less spreading. Remember that diffraction is strongest when the opening is comparable to the wavelength.

Question 2

1. smaller relative to $\lambda$, increasing diffraction (correct answer)
2. transmitting waves of larger amplitude, increasing diffraction
3. making the waves travel faster beyond the gap, increasing diffraction
4. increasing the wave frequency beyond the gap, increasing diffraction

Explanation: This question tests understanding of diffraction. Diffraction is the spreading of waves when they pass through openings, with maximum spreading occurring when the opening size is comparable to or smaller than the wavelength. The narrow gap between piers causes significant spreading because its width is about equal to λ, creating strong diffraction. The waves spread out in a semicircular pattern beyond the gap, reaching areas that would be in shadow if waves traveled only in straight lines. Choice B incorrectly suggests that wave amplitude affects diffraction, but diffraction depends solely on the geometric relationship between wavelength and opening size, not on wave intensity. Remember that diffraction is strongest when the opening is comparable to the wavelength.

Question 3

1. Use a narrower slit while keeping $\lambda$ the same (correct answer)
2. Increase the wave amplitude while keeping slit width and $\lambda$ the same
3. Increase the wave speed while keeping slit width and $\lambda$ the same
4. Use a wider slit while keeping $\lambda$ the same

Explanation: This question tests understanding of diffraction. Diffraction is the spreading of waves when they pass through an opening or around an obstacle, and the amount of spreading depends on the ratio of wavelength to opening size. When the slit width is comparable to the wavelength, significant diffraction occurs, with maximum spreading when the slit becomes narrower relative to the wavelength. The wave spreads out more with a narrower slit because the opening constrains the wavefront more severely, causing greater bending. Choice B incorrectly suggests amplitude affects diffraction, which is a common misconception - diffraction depends only on the wavelength-to-opening ratio, not on wave intensity. To maximize diffraction, make the opening size comparable to or smaller than the wavelength.

Question 4

1. Opening width $\approx \lambda$ (correct answer)
2. Opening width $\gg \lambda$
3. Higher transmitted amplitude at the same opening width
4. Higher wave speed at the same opening width

Explanation: This question tests understanding of diffraction. Diffraction is the spreading of waves when they pass through openings, with maximum spreading occurring when the opening size is comparable to the wavelength. When the opening width approximately equals λ, the transmitted waves spread into a nearly semicircular pattern, indicating strong diffraction. This happens because the opening acts almost like a point source, allowing waves to spread in all forward directions. Choice B incorrectly suggests that much larger openings cause more diffraction, but when the opening is much larger than the wavelength, waves pass through with minimal bending. The fundamental principle is that diffraction is strongest when the opening is comparable to the wavelength.

Question 5

1. unchanged, because it depends on $\lambda$ relative to $a$ (correct answer)
2. larger, because amplitude determines spreading angle
3. larger, because increased intensity increases diffraction
4. smaller, because brighter light travels faster

Explanation: This question tests understanding of diffraction. Diffraction patterns depend on the ratio of wavelength to slit width (λ/a), which determines the angular width of features like the central maximum. When only the light intensity is changed while keeping wavelength and slit width constant, the λ/a ratio remains unchanged, so the angular width of the central maximum stays the same. The pattern becomes brighter but maintains the same angular dimensions. Choice A incorrectly suggests intensity affects diffraction angle, but intensity only affects brightness, not the geometric spreading of the pattern. The key principle is that diffraction geometry depends only on the wavelength-to-opening ratio, not on wave intensity.

Question 6

1. It is greater, because the ratio $\lambda/w$ is larger (correct answer)
2. It is unchanged, because the slit width is the same
3. It is greater, because the wave amplitude is larger for longer wavelengths
4. It is smaller, because the wave speed is unchanged

Explanation: This question tests understanding of diffraction. Diffraction occurs when waves encounter an opening or obstacle, with the amount of spreading determined by the ratio λ/w, where λ is wavelength and w is the opening width. When wavelength increases while the slit width remains constant, the ratio λ/w increases, resulting in greater diffraction and more spreading of the waves. In this case, doubling the wavelength from λ to 2λ while keeping w constant doubles the ratio λ/w, causing increased spreading. Choice C incorrectly assumes that diffraction depends only on slit width, ignoring the crucial role of wavelength - this represents a misconception about what controls diffraction. The transferable strategy is that diffraction increases when wavelength increases relative to the opening size.

Question 7

1. Case 2, because a wider gap increases diffraction
2. Case 1, because the gap is much smaller than the wavelength (correct answer)
3. Case 2, because the waves have higher intensity through the gap
4. Case 1, because the wave speed decreases in narrower openings

Explanation: This question tests understanding of diffraction. Diffraction is the bending and spreading of waves as they pass through openings, with maximum spreading when the opening is comparable to or smaller than the wavelength. The ocean waves have wavelength 20 m, while Case 1 has a 5 m gap (much smaller than wavelength) and Case 2 has a 40 m gap (larger than wavelength). Case 1 produces greater diffraction because the gap (5 m) is much smaller than the wavelength (20 m), causing waves to spread dramatically into the sheltered region. Choice A incorrectly claims wider gaps increase diffraction, but actually narrower gaps relative to wavelength increase diffraction. The principle is that diffraction is strongest when the opening is comparable to or smaller than the wavelength.

Question 8

1. Setup V, because violet light travels faster in air
2. Setup V, because higher frequency increases diffraction
3. Setup R, because larger wavelength relative to $a$ increases diffraction (correct answer)
4. Setup R, because greater intensity causes more spreading

Explanation: This question tests understanding of diffraction. Diffraction is the spreading of light as it passes through slits, with the angular width of the central maximum proportional to λ/a (wavelength divided by slit width). Since red light has a longer wavelength than violet light (λR > λV) and both pass through identical slits of width a, red light has a larger λ/a ratio and produces a wider central maximum. Choice A incorrectly claims higher frequency increases diffraction, but higher frequency means shorter wavelength, which actually decreases diffraction for a fixed slit width. The key principle is that diffraction increases as wavelength increases relative to the opening size.

Question 9

1. Setup A, because $w$ is much smaller than $\lambda$ (correct answer)
2. Setup A, because the wave speed decreases in the opening
3. Setup B, because larger openings increase bending of waves
4. Setup B, because the transmitted amplitude is larger

Explanation: This question tests understanding of diffraction. Diffraction is the bending and spreading of waves as they pass through an opening, with the effect being most pronounced when the opening width w is small compared to the wavelength λ. In Setup A, w = λ/3 means the opening is much smaller than the wavelength, causing significant diffraction and spreading. In Setup B, w = 4λ means the opening is much larger than the wavelength, resulting in minimal diffraction with waves continuing mostly straight. Choice A represents a common misconception that larger openings cause more bending, when the opposite is true - smaller openings relative to wavelength cause greater diffraction. The key principle is that diffraction is strongest when the opening is comparable to or smaller than the wavelength.

Question 10

1. Trial 1, because $w$ is closer to (or smaller than) $\lambda$ (correct answer)
2. Trial 2, because a wider doorway transmits more intensity
3. Trial 1, because the frequency must be higher in the narrower doorway
4. Trial 2, because the sound speed in air is the same in both trials

Explanation: This question tests understanding of diffraction. Diffraction is the spreading of waves after passing through an opening, with the effect being strongest when the opening width w is comparable to or smaller than the wavelength λ. In Trial 1, w = 0.8λ means the doorway width is slightly smaller than the wavelength, producing significant diffraction. In Trial 2, w = 2.5λ means the doorway is much wider than the wavelength, resulting in minimal diffraction and the sound continuing mostly straight through. Choice A incorrectly focuses on transmitted intensity rather than the geometric relationship between opening size and wavelength - this misconception confuses diffraction with transmission. Remember that maximum diffraction occurs when the opening is about the same size as or smaller than the wavelength.

Question 11

1. wider, because the ratio $\lambda/a$ increases (correct answer)
2. unchanged, because diffraction depends only on wave speed
3. wider, because the light intensity at the slit is higher
4. narrower, because less light passes through the slit

Explanation: This question tests understanding of diffraction. Diffraction occurs when waves pass through openings, with the amount of spreading dependent on the ratio of wavelength to opening size (λ/a). For single-slit diffraction, the angular width of the central bright region is proportional to λ/a, meaning a smaller slit width produces a wider diffraction pattern. When the slit width decreases from 0.20 mm to 0.10 mm (halved), the ratio λ/a doubles, resulting in a wider central maximum. Choice C incorrectly claims diffraction depends only on wave speed, but it actually depends on the wavelength-to-slit ratio. Remember that diffraction effects become more pronounced as the opening becomes smaller relative to the wavelength.

Question 12

1. Case 2, because more wavefront passes through and spreads farther
2. Case 2, because the wave speed is higher for larger gaps
3. Case 1, because the gap width is comparable to $\lambda$ (correct answer)
4. Case 1, because the intensity is greater when the opening is smaller

Explanation: This question tests understanding of diffraction. Diffraction is the spreading of waves after passing through a gap, with the amount of spreading inversely related to the ratio of gap width to wavelength. When the gap width w equals the wavelength λ (Case 1), significant diffraction occurs because the opening is comparable to the wavelength. When w = 5λ (Case 2), the gap is much wider than the wavelength, resulting in minimal spreading as waves pass through mostly unchanged. Choice A incorrectly assumes that more wavefront passing through leads to more spreading, confusing the amount of wave energy with the geometric spreading angle - this is a common misconception. The strategy to remember is that diffraction effects are strongest when the opening size matches the wavelength.

Question 13

1. Opening X, because the amplitude must increase as the opening narrows
2. Opening Y, because more energy passes through a wider opening
3. Opening Y, because the wave speed increases in the opening
4. Opening X, because the opening is much smaller than $\lambda$ (correct answer)

Explanation: This question tests understanding of diffraction. Diffraction is the spreading of waves after passing through openings, with the amount of spreading inversely related to the ratio of opening size to wavelength. Opening X has width λ/4 (much smaller than the wavelength), while opening Y has width 2λ (much larger than the wavelength). When an opening is much smaller than the wavelength, waves spread out dramatically in all directions after passing through. Choice A incorrectly assumes more energy through a wider opening means more diffraction, but diffraction is about wave spreading, not energy transmission. The key principle is that diffraction is strongest when the opening is comparable to or smaller than the wavelength.

Question 14

1. Setup Q, because the wave speed decreases more at smaller openings
2. Setup P, because larger openings increase the bending of wavefronts
3. Setup Q, because the opening is smaller relative to $\lambda$ (correct answer)
4. Setup P, because greater transmitted intensity causes more spreading

Explanation: This question tests understanding of diffraction. Diffraction is the spreading of waves after passing through an opening, with the effect being strongest when the opening width w is small compared to the wavelength λ. In Setup Q, w = 0.4λ means the opening is much smaller than the wavelength, causing significant diffraction and spreading. In Setup P, w = 2λ means the opening is larger than the wavelength, resulting in less diffraction. Choice C incorrectly claims that larger openings increase wavefront bending, which is a common misconception - smaller openings relative to wavelength actually cause greater diffraction. The strategy is to identify which setup has the smaller w/λ ratio for maximum diffraction.

Question 15

1. more, because the wavelength-to-opening ratio increases (correct answer)
2. less, because longer wavelengths travel faster in air
3. more, because the sound intensity must be higher
4. less, because larger wavelength reduces diffraction

Explanation: This question tests understanding of diffraction. Diffraction is the spreading of waves through openings, with the amount of spreading determined by the wavelength-to-opening ratio. When the wavelength increases from λ to 2λ while the opening width stays fixed, the wavelength-to-opening ratio doubles, causing more diffraction and greater spreading of the emerging sound. This occurs because longer wavelengths diffract more through a given opening size. Choice D incorrectly claims larger wavelength reduces diffraction, which contradicts the fundamental principle that diffraction increases with wavelength for a fixed opening. Remember that diffraction is strongest when the opening is comparable to the wavelength.

Question 16

1. $650\,\text{nm}$ light because its intensity is higher
2. $450\,\text{nm}$ light because its amplitude is larger
3. $450\,\text{nm}$ light because its speed in air is greater
4. $650\,\text{nm}$ light because $\lambda/a$ is larger (correct answer)

Explanation: This question tests understanding of diffraction. Diffraction is the spreading of waves after passing through an opening, with the amount of spreading determined by the ratio λ/a (wavelength to slit width). Since both laser beams pass through the same slit width a, the beam with the larger wavelength will have a larger λ/a ratio and thus greater diffraction. The 650 nm light has a longer wavelength than 450 nm light, so it diffracts more. Choice B incorrectly suggests that light speed varies with wavelength in air, but all electromagnetic waves travel at the same speed c in vacuum or air. Remember: for a fixed opening, longer wavelength means more diffraction.

Question 17

1. Trial 2, because the amplitude on the screen is larger for smaller slits
2. Trial 2, because decreasing $w$ increases diffraction spreading (correct answer)
3. Trial 1, because a wider slit increases the angular spread
4. Trial 1, because the light speed is higher for larger slits

Explanation: This question tests understanding of diffraction. Diffraction causes light passing through a slit to spread out, creating a pattern with a central bright region whose width is inversely proportional to the slit width. When the slit width is reduced from w to w/2 while keeping wavelength constant, the ratio λ/w doubles, causing increased diffraction. This increased diffraction results in a wider central bright region on the screen in Trial 2. Choice A incorrectly assumes that wider slits cause more spreading, which is the opposite of what occurs - this represents a fundamental misconception about diffraction. The key principle is that narrower slits (smaller w) produce wider diffraction patterns.

Question 18

1. The spreading increases, because $w/\lambda$ decreases (correct answer)
2. The spreading decreases, because the transmitted intensity decreases
3. The spreading is unchanged, because the wave speed in air is unchanged
4. The spreading decreases, because the amplitude is smaller after the narrower gap

Explanation: This question tests understanding of diffraction. Diffraction is the spreading of waves through an opening, with the amount of spreading inversely related to the ratio w/λ, where w is gap width and λ is wavelength. When the gap width decreases from w = 1.2λ to w = 0.3λ, the ratio w/λ decreases from 1.2 to 0.3, causing significantly increased diffraction. This means the sound waves spread out more behind the wall with the narrower gap. Choice B incorrectly relates spreading to transmitted intensity rather than the geometric relationship between gap size and wavelength - this confuses diffraction with transmission effects. Remember that diffraction spreading increases as the opening becomes smaller relative to the wavelength.

Question 19

1. Setup 2, because higher wave speed increases diffraction
2. Setup 2, because the wave amplitude is larger after passing through
3. Setup 1, because the opening is smaller relative to $\lambda$ (correct answer)
4. Setup 1, because greater intensity causes more diffraction

Explanation: This question tests understanding of diffraction. Diffraction is the spreading of waves as they pass through openings, and this spreading is most pronounced when the opening size is comparable to or smaller than the wavelength. When the opening is much larger than the wavelength, waves pass through with minimal spreading, while openings similar to or smaller than the wavelength cause significant spreading. In this problem, Setup 1 has an opening of 0.5λ (smaller than the wavelength), while Setup 2 has an opening of 3λ (much larger than the wavelength). Choice A incorrectly suggests wave speed affects diffraction, but wave speed doesn't determine the amount of spreading. The key strategy is to compare the ratio of wavelength to opening size: maximum diffraction occurs when the opening is about the same size as or smaller than the wavelength.

Question 20

1. The $0.80\ \text{m}$ wavelength tone, because $\lambda$ is closer to the doorway width (correct answer)
2. The $0.20\ \text{m}$ wavelength tone, because higher frequency increases diffraction
3. The $0.20\ \text{m}$ wavelength tone, because it travels faster in air
4. Both tones equally, because loudness determines diffraction

Explanation: This question tests understanding of diffraction. Diffraction is the bending and spreading of waves as they pass through openings, with greater spreading occurring when the wavelength is comparable to the opening size. The doorway width is 0.90 m, and we compare two sound waves: one with wavelength 0.80 m (close to the doorway width) and another with wavelength 0.20 m (much smaller than the doorway). The 0.80 m wavelength will diffract more because its wavelength is nearly the same as the opening width. Choice B incorrectly suggests higher frequency increases diffraction, but actually lower frequency (longer wavelength) increases diffraction when the opening size is fixed. The principle to remember is that diffraction is strongest when the opening is comparable to the wavelength.