Light and Sound Quiz

A boy claps his hands and hears the echo after 2 seconds. If the speed of sound in air is 340 m/s, how far away is the reflecting surface?

1. 170 m
2. 340 m
3. 510 m
4. 680 m

Answer: (b) 340 m

A light ray passes from water into air. Which of the following best describes its behaviour?

1. It speeds up and bends toward the normal.
2. It slows down and bends toward the normal.
3. It speeds up and bends away from the normal.
4. It slows down and bends away from the normal.

Answer: (c) It speeds up and bends away from the normal.

Why is the siren of an ambulance heard faintly from far away, but becomes louder as it approaches?

1. The ambulance continuously increases its siren volume
2. Sound intensity increases as distance decreases
3. Sound waves stretch out as the ambulance moves
4. Higher-pitched sounds travel faster than lower-pitched sounds.

Answer: (b) Sound intensity increases as distance decreases

A sound source produces a frequency of 500 Hz. What will happen to the wavelength if the sound travels from air to water?

1. It will increase.
2. It will decrease.
3. It will remain the same.
4. It depends on the amplitude of the wave

Answer: (a) It will increase.

In a room, a man stands in front of a large concave mirror positioned far away from him. When he moves towards the mirror, how does the size of his image change?

1. Remains the same
2. Gradually increases
3. Gradually decreases
4. First increases, then decreases

Answer: (d) First increases, then decreases

If a concave mirror produces a real, inverted, and magnified image of an object, which of the following is a valid position for the object?

1. At the centre of curvature
2. Between the pole and the focus
3. Between the focus and the centre of curvature
4. Beyond the centre of curvature

Answer: (c) Between the focus and the centre of curvature

Consider the assertion and reason given below and choose the correct option. Assertion: Echoes cannot be heard clearly in a room with thick curtains and carpets. Reason: Soft materials absorb sound waves instead of reflecting them.

1. Both Assertion and Reason are correct, and Reason is the correct explanation.
2. Both Assertion and Reason are correct, but Reason is not the correct explanation.
3. Assertion is correct, but Reason is incorrect.
4. Assertion is incorrect, but Reason is correct.

Answer: (a) Both Assertion and Reason are correct, and Reason is the correct explanation.

A student claps her hands in a large hall. She hears an echo only when standing at least 17 m away from the wall but not closer. Why does she not hear an echo when closer? A. Sound travels too fast for the echo to return. B. The time gap between the original sound and the echo is too small to detect. C. The sound wave gets absorbed by the wall. D. Echoes are only possible at distances greater than 20 m.

1. Only A
2. Only B
3. Only A and C
4. A, B and C

Answer: (b) Only B

If the speed of sound is 340 m/s, the minimum distance of a reflecting surface to hear an echo is given in the table for different time delays. Which of these entries is correct? Time Delay (s) Minimum Distance (m) 1 0.1 17 2 0.2 34 3 0.3 51

1. Only 1
2. Only 2
3. Only 2 and 3
4. 1, 2 and 3

Answer: (d) 1, 2 and 3

The table below shows how different materials reflect and absorb sound. Which material is best suited for recording studios and why? Material Reflection Coefficient (%) Absorption Coefficient (%) Common Use Concrete 80 20 Building Walls Foam 10 90 Soundproofing Water 50 50 Sonar Applications

1. Concrete, because it reflects most of the sound.
2. Foam, because it enhances sound reflection.
3. Water, because it balances reflection and absorption.
4. Foam, because it absorbs most of the sound.

Answer: (d) Foam, because it absorbs most of the sound.