# Waves Multiple Choice Questions

Q1. Waves produced in a cylinder containing a liquid by moving its piston back and forth. The wave motion in this case is:

1. transverse
2. longitudinal
3. combination of both transverse and longitudinal
4. None of the above

Answer :- (3) combination of both transverse and longitudinal

Q2. If you are standing next to the road, why does the pitch of the siren of police car change as it comes toward you?

1. Relative velocity changes as its angle with respect to you changes as the police car approaches you .
2. Speed of sound increases
3. The pitch is constant until the ambulance passes by
4. The pitch seems to changes, due to changing in air pressure

Answer :- (1) Relative velocity changes as its angle with respect to you changes as the police car approaches you .

Q3. The apparent frequency of the whistle of an engine changes in the ratio 9:8 as the engine passes a stationary observer. If the velocity of the sound is 340 ms-1, then the velocity of the engine is:

1. 40 m/s
2. 20 m/s
3. 340 m/s
4. 180 m/s

Q4. Two sound sources fixed at a given distance apart are emitting sound each of wavelength λ. A Listener moves with a velocity v0 along the line joining the two sources, the number of beats heard by him per second is

1. 2v0
2. v0/2λ
3. 4v0
4. v0/3λ

Q5. Doppler effects would not hold for

1. Electromagnetic waves
2. Micro waves
4. Circular waves

Q6. Doppler effect would take place in case of

1. Source and listener both move in same direction with the same speed
2. When both source and listener both are at rest and wind is blowing
3. When one of the source or listener is at the centre of a circle, while the other is moving on it with uniform speed
4. Detecting new planets with help of Doppler shift of light

Answer :- (4) Detecting new planets with help of Doppler shift of light

Q7. A tube closed at one end and containing air produces, when excited, the fundamental note of frequency 512 Hz. If the tube is open at both ends the fundamental frequency that can be excited is ( in Hz ):

1. 1024
2. 512
3. 256
4. 128

Q8. Speed of the sound in a perfectly rigid rod would be

1. Dubbed
2. Damp
3. Oscillating
4. Infinite

Q9. How to find that two tuning forks of the same musical note were exactly the same?

1. Strike them both at the same time to verify there is no beat frequency
2. Compare each with the correct piano key
3. Labels in tuning forks are same
4. Both have equal weight and shape

Answer :- (1) Strike them both at the same time to verify there is no beat frequency

Q10. What would be the fundamental frequency of a 20 cm long close ended pipe? Would it resonantly be excited by a 430 Hz source?(Take speed of sound as 340 m/s)

1. 425 Hz, yes
2. 415 Hz, yes
3. 400 Hz, no
4. 430 Hz, yes

Answer :- (1) 425 Hz, yes

Q11. A steel wire 120 cm long has mass 12 g attached to it. If the wire is under a tension of 150N, what is the speed of transverse wave in the wire?

1. 1.65 m/s
2. 1.24 m/s
3. 1.22 m/s
4. 2.12 m/s

Q12. The number of beats produced per second by the vibrations x= A sin (420 πt) and x= A sin (424 πt) is

1. 4
2. 6
3. 1
4. 2

Q13. Two guitar strings A and B are slightly out of tune and produce beats of frequency 6 Hz. The tension of the string was found to decrease to 4 Hz. What is the original frequency of B if the frequency of A is 430 Hz?

1. 435 Hz
2. 424 Hz
3. 436 Hz
4. 420 Hz

Q14. When a travelling wave is reflected at a rigid boundary the reflected wave has ______, but reflection at an open boundary has ________.

1. no phase change, phase reversal
2. phase reversal, no phase change
3. no phase change, no phase change
4. phase reversal, phase reversal

Answer :- (2) phase reversal, no phase change

Q15. Which medical instrument uses Doppler effect?

1. Stethoscope
2. Ultrasound machine
3. Echocardiogram
4. MRI machine

Q16. A standing wave is formed when ____.

1. a wave reflects due to changes in the properties of the medium.
2. a wave reflects off a  wall
3. air is compressed in a cylinder
4. two identical waves moving in opposite directions along the same medium interfere

Answer :- (4) two identical waves moving in opposite directions along the same medium interfere

Q17. Which of the following waves can be polarized?

1. Light waves
2. Sound waves
3. Electro magnetic waves
4. Water waves

Q18. Standing waves result from the superposition of two waves that have:

1. the same amplitude, frequency, and direction of propagation
2. the same amplitude and frequency and opposite directions of propagation
3. the same amplitude, slightly different frequencies, and the same direction of propagation
4. the same amplitude, slightly different frequencies, and opposite directions of propagation

Answer :- (2) the same amplitude and frequency and opposite directions of propagation

Q19. Maximum destructive inference between two waves occurs when the waves are out of the phase by

Q20. Two trains A and B approach a station from opposite sides, sounding their whistles.  A stationary observer on the platform hears no beats.  If the velocities of A and B are 15 m/s and 30 m/s respectively and the real frequency of the whistle of B is 600 Hz, the real frequency of the whistle of A is (Velocity of sound = 330 m/s).

1. 630 Hz
2. 600 Hz
3. 660 Hz
4. 570 Hz

Q21. A travelling wave in a stretched string is described by the equation; y = a sin ( Kx – ωt). The maximum particle velocity is:

1. Aω
2.   ω / k
3. Dω/dk
4. x/ω

Q22. Wavelength of a progressive wave is the distance between two

1. consecutive points of the same phase at a given time.
2. alternate points of the same phase at a given time
3. consecutive points out of phase by 180 degrees
4. consecutive points out of phase by 90 degrees

Answer :- (1) consecutive points of the same phase at a given time.

Q23. If you blow air over the top of a fairly large drinking straw you can hear a fundamental frequency due to a standing wave being set up in the straw. What happens to the fundamental frequency if while blowing you cut the straw in half with a pair of scissors?

1. The fundamental frequency decreases
2. The fundamental frequency increases
3. The fundamental frequency remains unchanged
4. Insufficient information

Answer :- (2) The fundamental frequency increases

Q24. What causes the rolling sound of thunder?

1. Reflection of waves
2. Air currents
3. Refraction of waves
4. High amplitude

Answer :- (1) Reflection of waves

Q25. A spectral line of wave length 5000 A.U in the light coming from a distant star is observed to be shifted to 5004 A.U.  The component of the recessional velocity of the star along the line of sight is :

1. 1.4 x 105 m/s
2. 1.8 x 105 m/s
3. 2.0 x 105 m/s
4. 2.4 x 105 m/s

Answer :- (4) 2.4 x 105 m/s

Q26. A cylindrical tube, open at both ends, has a fundamental frequency f in air. The tube is dipped vertically in water so that half of it is in water. The fundamental frequency of the air-column is now:

1. f/2
2. 3f/2
3. f
4. 2f

Q27. Waves associated with moving protons, electrons, neutrons, atoms are known as

1. Electromagnetic waves
2. Gamma rays
3. Matter waves
4. Matter waves

Q28. Pure sound notes from two sources make the molecules of air at a location vibrate simple harmonically in accordance with the equations. y1 = 0.008 sin (604 π t) and y2 = 0.007 sin (610 π t) respectively. The number of beats heard by a person at the location will be:

1. 1
2. 2
3. 3
4. 4

Q29. In a wave, which quantity is transferred from one point to the other?

1. matter
2. energy
3. wavelength
4. frequency

Q30. To the nearest order of magnitude, how many times greater than the speed of sound is the speed of light?

1. 104
2. 108
3. 106
4. 1012

Q31. On adding two sine waves that are exactly the same, what would be the result?

1. an identical sine wave
2. an identical sine wave with half the amplitude
3. an identical sine wave with double the amplitude
4. an identical sine wave with double the frequency

Answer :- (3) an identical sine wave with double the amplitude

Q32. A radio station broadcasts programs at wave frequency 20 Megacycles/sec. What would be their wavelength?

1. 5 m
2. 15 m
3. 10 m
4. 20 m

Q33. Beats are produced by the superposition of two harmonic waves if:

1. their amplitudes and frequencies are equal
2. their amplitudes are the same but their frequencies differ slightly
3. their frequencies differ slightly even if their amplitudes are not equal
4. both (b) and (c)

Answer :- (4) both (b) and (c)

Q34. A sound source of frequency 600 Hz is moving towards an observer with velocity 20 m/s. The speed of sound is 340m/s. The frequency heard by observer will be

1. 30 Hz
2. 630.5 Hz
3. 637.5 Hz
4. 63.5 Hz

Q35. What types of waves can not be produced in liquids and gases?

1. x-rays
2. transverse waves
3. longitudinal waves
4. electro magnetic waves

Q36. Graph between speed of sound and pressure of gas would be

1. Parabola
2. Curved line
3. Straight line
4. Hyperbola

Q37. A person moves away with constant velocity ‘v0‘ from a stationary train which blows its whistle.  The ratio of the real frequency of the whistle to the apparent frequency as measured by the person is 1.25.  If the person is stationary and the whistle is moving away from the person with the same velocity ‘v0‘, the ratio of the real frequency of the whistle to the apparent frequency as measured by the person will be

1. 1.2
2. 1.25
3. 1.4
4. 1.45

Q38. A wave traveling along a string is described by
y (x,t)=0.005 sin(95.0x-4.0t)
what would be its angular wave number, k, and wavelength, λ?

1. 6.01m
2. 6.66 cm
3. 6.61cm
4. 6.61m

Q39. What is the range of frequency of audible sound?

1. 20Hz to 20000hz
2. 2Hz to 200Hz
3. 20 Hz to 2000Hz
4. 5Hz to 5000hz

Answer :- (1) 20Hz to 20000hz

Q40. Phenomenon of beats is not used in

1. Tuning musical instruments
2. Designing low frequency oscillators