CBSE Class 11 Physics Waves MCQs Set C

Question: A source of frequency u gives 5 beats/second when sounded with a source of frequency 200 Hz. The second harmonic of frequency 2u of source gives 10 beats/second when sounded with a source of frequency 420 Hz. The value of u is
a) 205 Hz
b) 195 Hz
c) 200 Hz
d) 210 Hz.
Answer: a

Question: A sonometer wire of length l vibrates in fundamental mode when excited by a tuning fork of frequency 416 Hz. If the length is doubled keeping other things same, the string will
a) vibrate with a frequency of 416 Hz
b) vibrate with a frequency of 208 Hz
c) vibrate with a frequency of 832 Hz
d) stop vibrating
Answer: a

Question: Water waves produced by a motorboat sailing in water are
a) neither longitudinal nor transverse
b) both longitudinal and transverse
c) only longitudinal
d) only transverse
Answer: b

Question: A stationary wave is represented by y = Asin (100t) cos (0.01x), where y and A are in millimetres, t is in seconds and x is in metres. The velocity of the wave is
a) 104 m/s
b) not derivable
c) 1 m/s
d) 102 m/s
Answer: a

Question: The two nearest harmonics of a tube closed at one end and open at other end are 220 Hz and 260 Hz. What is the fundamental frequency of the system?
a) 20 Hz
b) 30 Hz
c) 40 Hz
d) 10 Hz
Answer: a

Question: Two cars moving in opposite directions approach each other with speed of 22 m/s and 16.5 m/s respectively. The driver of the first car blows a horn having a frequency 400 Hz. The frequency heard by the driver of the second car is [velocity of sound 340 m/s] :-
a) 361 Hz
b) 411 Hz
c) 448 Hz
d) 350 Hz
Answer: c

Question: A siren emitting a sound of frequency 800 Hz moves away from an observer towards a cliff at a speed of 15ms^–1. Then, the frequency of sound that the observer hears in the echo reflected from the cliff is : (Take velocity of sound in air = 330 m^s–1)
a) 765 Hz
b) 800 Hz
c) 838 Hz
b) 885 Hz
Answer: c

Question: Two vibrating tuning forks produce progressive waves given by Y1 = 4 sin 500 pt and Y2 = 2 sin 506 pt. Number of beats produced per minute is
a) 360
b) 180
c) 60
d) 3
Answer: b

Question: An organ pipe open at one end is vibrating in first overtone and is in resonance with another pipe open at both ends and vibrating in third harmonic. The ratio of length of two pipes is
a) 1 : 2
b) 4 : 1
c) 8 : 3
d) 3 : 8
Answer: a

Question: The total mechanical energy of a spring-mass system in simple harmonic motion is m 2A2 E = 1/2 mω2A2 . Suppose the oscillating particle is replaced by another particle of double the mass while the amplitude A remains the same. The new mechanical energy will
a) become 2E
b) become E/2
c) become √2E
d) remain E
Answer: d

Question: Sound waves travel at 350 m/s through a warm air and at 3500 m/s through brass. The wavelength of a 700 Hz acoustic wave as it enters brass from warm air
a) decreases by a factor 10
b) increases by a factor 20
c) increases by a factor 10
d) decreases by a factor 20
Answer: c

Question: Three sound waves of equal amplitudes have frequencies (n – 1), n, (n + 1). They superimpose to give beats. The number of beats produced per second will be
a) 1
b) 4
c) 3
d) 2
Answer: d

Question: Two sources of sound placed close to each other are emitting progressive waves given by y1 = 4 sin 600 pt and y2 = 5 sin 608 pt. An observer located near these two sources of sound will hear
a) 4 beats per second with intensity ratio 25 : 16 between waxing and waning.
b) 8 beats per second with intensity ratio 25 : 16 between waxing and waning
c) 8 beats per second with intensity ratio 81 : 1 between waxing and waning
d) 4 beats per second with intensity ratio 81 : 1 between waxing and waning
Answer: d

Question: Two sources of sound placed close to each other, are emitting progressive waves given by y1 = 4sin600pt and y2 = 5sin608pt An observer located near these two sources of sound will hear
a) 4 beats per second with intensity ratio 25 : 16 between waxing and waning.
b) 8 beats per second with intensity ratio 25 : 16 between waxing and waning.
c) 8 beats per second with intensity ratio 81 : 1 between waxing and waning.
d) 4 beats per second with intensity ratio 81 : 1 between waxing and waning.
Answer: d

Question: Two sources of sound placed close to each other, are emitting progressive waves given by y1 = 4sin600pt and y2 = 5sin608pt An observer located near these two sources of sound will hear
a) 4 beats per second with intensity ratio 25 : 16 between waxing and waning.
b) 8 beats per second with intensity ratio 25 : 16 between waxing and waning.
c) 8 beats per second with intensity ratio 81 : 1 between waxing and waning.
d) 4 beats per second with intensity ratio 81 : 1 between waxing and waning.
Answer: d

Question: Standing waves are produced in 10 m long stretched string. If the string vibrates in 5 segments and wave velocity is 20 m/s, the frequency is
a) 5 Hz A
b) 10 Hz
c) 2 Hz
d) 4 Hz
Answer: a

Question: A stretched string resonates with tuning fork frequency 512 Hz when length of the string is 0.5 m. The length of the string required to vibrate resonantly with a tuning fork of frequency 256 Hz would be
a) 0.25 m
b) 0.5 m
c) 1 m
d) 2 m
Answer: c

Question: Which of the following statements are true for wave motion?
a) Mechanical transverse waves can propagate through all mediums
b) Longitudinal waves can propagate through solids only
c) Mechanical transverse waves can propagate through solids only
d) Longitudinal waves can propagate through vacuum
Answer: c

Question: A car is moving towards a high cliff. The car driver sounds a horn of frequency f. The reflected sound heard by the driver has as frequency 2f. If v be the velocity of sound, then the velocity of the car, in the same velocity units, will be
a) v /2
b) v /Ö2
c) v /3
d) v /4
Answer: c

Question: The second overtone of an open organ pipe has the same frequency as the first overtone of a closed pipe L metre long. The length of the open pipe will be
a) L
b) 2L
c) L/2
d) 4L
Answer: b

Question: A source of sound produces waves of wavelength 60 cm when it is stationary. If the speed of sound in air is 320 m s^–1 and source moves with speed 20 m s^–1, the wavelength of sound in the forward direction will be nearest to
a) 56 cm
b) 60 cm
c) 64 cm
d) 68 cm
Answer: a

Question: A speeding motorcyclist sees trafic jam ahead of him. He slows down to 36 km/hour. He finds that traffic has eased and a car moving ahead of him at 18 km/hour is honking at a frequency of 1392 Hz. If the speeds of sound is 343 m/s, the frequency of the honk as heard by him will be :
a) 1332 Hz
b) 1372 Hz
c) 1412 Hz
d) 1464 Hz
Answer: c

Question: cm is equal to the second overtone of an organ pipe open at both the ends. The length of organ pipe open at both the ends is
a) 100 cm
b) 120 cm
c) 140 cm
d) 80 cm
Answer: a

Question: Velocity of sound waves in air is 330 m/s. For a particular sound wave in air, a path difference of 40 cm is equivalent to phase difference of 1.6p. The frequency of this wave is
a) 165 Hz
b) 150 Hz
c) 660 Hz
d) 330 Hz
Answer: c

Question: Speed of sound wave in air
a) is independent of temperature
b) increases with pressure
c) increases with increase in humidity
d) decreases with increase in humidity
Answer: c

Question: Change in temperature of the medium changes
a) frequency of sound waves
b) amplitude of sound waves
c) wavelength of sound waves
d) loudness of sound waves
Answer: c

Question: An air column, closed at one end and open at the other, resonates with a tuning fork when the smallest length of the column is 50 cm. The next larger length of the column resonating with the same tuning fork is :
a) 66.7 cm
b) 100 cm
c) 150 cm
d) 200 cm
Answer: c

Question: Wave has simple harmonic motion whose period is 4 seconds while another wave which also possesses simple harmonic motion has its period 3 seconds. If both are combined, then the resultant wave will have the period equal to
a) 4 s
b) 5 s
c) 12 s
d) 3 s
Answer: c