1. [2080 R] If the source of sound and the listener move in the same direction with same velocity equal to half the velocity of sound. What is the change in frequency?
   a. 0%
   b. 25%
   c. 50%
   d. 100%
2. [2079 O] In which frequency range the infrasonic wave lies?
   a. (10 – 20) Hz
   b. (30 – 40) Hz
   c. (20 – 30) Hz
   d. (50 – 60) Hz
3. [2079 V] The intensity of sound ‘I’ and amplitude of vibration ‘a’ are related as,
   a. [latex]I\propto a[/latex]
   b. [latex]I\propto a^2[/latex]
   c. [latex]I\propto \frac{1}{a}[/latex]
   d. [latex]I\propto \frac{1}{a^2}[/latex]

Answers:

1.a

2.a

3.b

New Course

1. [2081 GIE ‘A’] Define Doppler’s effect. Write two uses of it. [1+1]
2. [2081 GIE ‘B’] Sound waves are called pressure waves. Why? [2]
3. [2081 GIE ‘B’] In what condition Doppler’s effect is not applicable.   [1]
4. [2081 D] Sound waves are called pressure wave. Why?                    [1]
5. [2081 D] Define one bel. What is threshold of hearing?                    [2]
6. [2081 D] Derive an expression for apparent frequency heard by a listener while moving towards stationary source of sound. [2]
7. [2080 GIE ‘A’]
   a. What is Doppler’s effect? Calculate the apparent frequency when a source moves towards a stationary observer. [1 + 2]
   b. Why sound waves are also called pressure waves? Explain. [2]

8. [2080 GIE Set-B]

1. Sound waves are also called pressure waves. Why? [2]
2. What is Doppler’s effect? [1]

9. [2080 Set-P] In the given figure below, figure (i) represents a situation that both source of sound (S) and Listener (L) are at rest position ‘S’ and ‘L’ respectively. Figure (ii) represents relative motion between moving source and stationary listener.

1. Does the pitch of sound changes to the listener in second case? Justify. [1]
2. Develop an expression to support your answer in (i). [3]

10. [2080 Set-P] Write any two properties of medium which is necessary for the propagation of sound. [1]
11. [2079 GIE Set-A]

1. What is Doppler’s effect? [1]
2. Deduce the formula for the apparent frequency of sound wave when the source is moving towards the stationary listener. [2]

12. [2079 GIE Set-B]

1. Why does an empty vessel produce louder sound than the filled one? [2]
2. Deduce an expression of apparent frequency of sound wave when the source of sound is moving towards a stationary observer. [2]
3. Define one bel. [1]

13. [2079 Set-O]

1. State Doppler’s effect. [1]
2. Derive the apparent frequency of sound when an observer moves towards a stationary source. [2]

14. [2079 Set-V]

1. What do you mean by Doppler’s effect. [1]
2. How is it that one can recognize a friend from his voice without seeing him? [2]            
3. Write down the factors on which the speed of sound in air depends. [2]

Old Course

SHORT ANSWER QUESTION

15. [2078 Set-C] What are infrasonic and ultrasonic waves?
16. [2077 Set-D] What is quality of sound?
17. [2076 GIE Set-A] Can you distinguish two notes, one produced by violin and the other by a sitar, having the same frequency? Explain.
18. [2076 GIE Set-B] How can bats fly around without colliding with objects that come in their way?
19. [2076 Set-B, 2073 ‘S’] An empty vessel sounds more than a filled one when it is struck. Why?
20. [2076 Set-C] Sound waves are called pressure waves. Why?
21. [2075 ‘S’, 2072 Set-E] Define one bel.
22. [2075 ‘S’, 2074 ‘S’, 2074 Set-A] Longitudinal waves are called pressure waves. Why?
23. [2075 Set-A] Justify the proverb “An empty vessel makes much noise”.
24. [2075 Set-B] Why is the voice of a woman more intelligible than that of a man?
25. [2074 ‘S’] What is meant by ultrasonic and infrasonic waves?
26. [2073 Set-D] Explain the difference in characteristics between ultrasonic and supersonic waves.
27. [2072 Set-C] Whistle of an approaching train is shriller. Why?
28. [2072 Set-D] If the pressure amplitude of a sound wave is halved, by what factor does the intensity of the wave change?
29. [2072 Set-E] A tuning fork has two prongs. Why?

LONG ANSWER QUESTION

30. [2076 GIE Set-A] Define intensity of sound and show that [latex]I = \frac{1}{2}\rho vr^2\omega^2[/latex] where symbols have their usual meaning.
31. [2076 GIE Set-B] Describe sound wave as a pressure wave and deduce an expression for the pressure amplitude.
32. [2076 Set-B, 2075 Set-A] What is Doppler’s effect? Derive an expression for the apparent frequency received by a stationary observer when a source is moving away from him.
33. [2076 Set-C, 2075 Set-B, 2074 Set-B, 2073 Set-D, 2075 ‘S’] What is Doppler’s effect in sound? Obtain an expression for the apparent frequency when both source of sound and observer move towards each other.
34. [2075 Set-A] What is Doppler’s effect? Obtain an expression for the apparent pitch when a source moves away from a stationary observer.
35. [2073 ‘S’] Show that the intensity of sound for a given frequency is directly proportional to the square of amplitude of vibration.
36. [2072 Set-C] Describe sound wave as a pressure wave and deduce an expression for the pressure amplitude.
37. [2072 Set-E] What is Doppler’s effect? Find the change in frequency when an observer moves towards a stationary source and then moves away from the source.

New Course

1. [2082] A train is approaching a cliff at 10 m/s. The driver sounds a whistle of frequency 600 Hz. What will be the frequency of echo as heard by the driver? (Velocity of sound in air = 340 [latex]ms^{-1}[/latex]. [3] Ans: 636.36 Hz
2. [2081 GIE Set-A] A car is sounding a horn of frequency 500 Hz and travelling towards a stationary observer with speed 20 m/s. What is apparent frequency heard by the observer? (Velocity of sound in air = 340 m/s).      [3] Ans: 531.25 Hz
3. [2081 GIE Set-B] A source having frequency 240 Hz is moving towards an observer with a speed of 10 m/s. When the observer is moving away the source with a velocity of 30 m/s, then find the apparent frequency heard by observer if velocity of sound in air is 340 m/s. [3] Ans: 225.5 Hz
4. [2081 Set-B/C] A car is sounding its horn has a frequency 400 Hz and travelling towards a stationary traffic post. A traffic police at the post detects the change in frequency of 60 Hz when the car crosses him. Find the velocity of car if velocity of sound in air is 340 [latex]ms^{-1}[/latex]. [3] Ans: 25 m/s
5. [2081 Set-D] A car is approaching towards a cliff at a speed of 20 m/s. The driver sounds a whistle of frequency 800 Hz. Calculate the frequency of echo as heard by the car driver. [Velocity of sound in air 350 m/s]                  [3] Ans: 896.97 Hz
6. [2080 GIE Set-B]

1. A sound source producing 1.00 KHz waves moves toward a stationary listener at one-half the speed of sound. What frequency will the listener hear?   [2] Ans: 2KHz
2. Suppose instead that the source is now stationary and the listener moves towards the source at one-half the speed of sound. What frequency will the listener hear?       [2] Ans: 1.5 KHz

7. [2079 GIE Set-A] A car travelling at 20 [latex]ms^{-1}[/latex] sounds its horn which has a frequency of 600 Hz. What frequency is heard by a stationary distant observer as the car approaches? Velocity of sound = 340 m/s.                    [2] Ans: 637.5 Hz
8. [2079 Set-O] A stationary motion detector sends sound waves of 150 KHz towards a truck approaching at a speed of 120 km/hr. What is the frequency of wave reflected back to detector? (Velocity of sound in air = 340 m/s)          [2] Ans: 182.6 KHz

Old Course

9. [2078 Set-C] A train approaching a tunnel in a cliff face at 25 [latex]ms^{-1}[/latex] is sounding a whistle of frequency 800 Hz. What will be the apparent frequency of the echo from the cliff heard by the driver? (velocity of sound in air = 332 m/s)             Ans: 930.3 Hz
10. [2075 ‘S’, 2074 Set-A] The driver sounds a whistle of frequency 800 Hz. What will be the frequency of the echo as heard by the driver? [Velocity of sound in air = 350 m/s]. Ans: 896.97 Hz
11. [2073 Set-C] A car travelling with a speed of 60 Kmhr^-1 sounds a horn of frequency 500 Hz. The sound is heard in another car travelling behind the first car in the same direction with a speed of 80 Kmhr^-1. What frequencies will the driver of the second car hear before and after overtaking the first car if the velocity of sound is 340 m/s? Ans: 507.8 Hz and 491.4 Hz
12. [2072 Set-D] A stationary motion detector sends sound waves of 150 KHz towards a truck approaching at a speed of 120 km/hr. What is the frequency of wave reflected back to detector? (Velocity of sound in air = 340 m/s). Ans: 182.6 KHz