Sound (Classroom Sheet)

1. Two interfering waves of the same frequency have an intensity ratio 16 : 1. The ratio of intensities at the maxima and minima is :
(a) 25/16 (b) 9 (c) 4 (d) 25/9
2. Two interfering waves of the same frequency have amplitudes in the ratio 1 : 3. If the intensity of the first wave is I, the intensity at
maxima of interference is (a) 16 I (b) 8I (c) 4 I (d) 64 I
3. When beats are produced by two waves, viz, y1 = A sin 1000 t and y2 = A sin 1008  t, the beat frequency will be
(a) 4 Hz (b) 8 Hz (c) 4  Hz (d) 8  Hz
4. The speed of sound in a gas in which two waves of wavelengths 50 cm and 50.4 produce 6 beats per second is :
(a) 338 m/s (b) 350 m/s (c) 378 m/s (d) 400 m/s
5. Wavelengths of two notes in air are 80/195 and 80/193 m. Each note produces 5 beats/s with a third note a fixed frequency. The speed of
sound in air is : (a) 300 m/s (b) 340 m/s (c) 375 m/s (d) 400 m/s
6. 65 tuning forks are arranged in order of increasing frequency. Any two successive forks produce 4 beats/s when sounded together. If the
last fork gives an octave of the first, the frequency of the first is : (a) 252 Hz (b) 256 Hz (c) 260 Hz (d) 264 Hz
7. When a tuning fork A of frequency 100 Hz is sounded with a tuning fork B, the number of beats per second is 2. On putting some wax
in the prongs of B, the number of beats per second becomes 1. The frequency of the fork B is :
(a) 98 Hz (b) 99 Hz (c) 101 Hz (d) 102 Hz
8. A tuning fork whose frequency as given by the manufacturer is 512 Hz is being tested using an accurate oscillator. It is found that they
produce 2 beats per second when the oscillator reads 514 Hz, and 6 beats per second when it reads 510 Hz. The actual frequency of the
fork is : (a) 508 Hz (b) 512 Hz (c) 516 Hz (d) 518 Hz
9. Two sounding bodies producing progressive waves given by y1 = 4 sin 400 t and y2 = 3 sin 404 t, where t is in seconds, are situated
near the ears of a person. The person will hear
(a) 2 beats per second with intensity ratio 4/3 between maxima and minima
(b) 2 beats per second with intensity ratio 49 between maxima and minima
(c) 4 beats per second with intensity ratio 7 between maxima and minima
(d) 4 beats per second with intensity ratio 4/3 between maxima and minima
10. A sonometer wire is in resonance with a tuning fork. Keeping the same tension, the length of the wire between the bridges is doubles. It
can still be in resonance with the tuning fork provided it vibrates in
(a) 2 segments (b) 3 segments (c) 4 segments (d) 6 segments
11. In Melde’s experiments a string of length 0.8 m and mass 1.0 g vibrates in 4 segments with the tension in the string is 0.4 kg wt. The
frequency of the fork is : (a) 70 Hz (b) 90 Hz (c) 140 Hz (d) 180 Hz
12. A vibrating stretched string resonates with a tuning fork of frequency 512 Hz when the 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) 0.75 m (c) 1.0 m (d) 2.0 m
13. Velocity of sound in air is 320 m/s. A pipe closed at one end has a length of 1 m. Neglecting end corrections the air column in the pipe
can resonate for sound of frequency (a) 80 Hz (b) 240 Hz (c) 320 Hz (d) 400 Hz
14. An organ pipe P1 closed at one end and vibrating in its first overtone and another pipe P 2 open at both ends and vibrating in its third
overtone, are in resonance with a given tuning fork. The ratio of the length of P 1 to that of P2 is
(a) 8/3 (b) 3/8 (c) 1/2 (d) 1/3
15. For the stationary wave y = 4 sin (x/15) cos (96 t), the distance between a node and the next antinode is :
(a) 7.5 units (b) 15 units (c) 22.5 units (d) 30 units
16. A tuning fork of frequency 340 Hz is vibrated just above a cylindrical tube of length 120 cm. Water is slowly poured in the tube. If the
speed of sound in air is 340 m/s, Then the minimum height of water required for resonance is :
(a) 25 cm (b) 45 cm (c) 75 cm (d) 95 cm
17. Two tuning forks A and B give 5 beats/s. A resonates with a column of air 15 cm long, closed at one end and B with a column 30.5 cm
long, open at both ends. Neglecting end correction, the frequencies of A and B are respectively
(a) 300 Hz, 295 Hz (b) 295 Hz, 300 Hz (c) 305 Hz, 300 Hz (d) 300 Hz, 305 Hz
18. A column of air at 51C and a tuning fork produce 4 beats/s when sounded together. As the temperature of the air column is decreased,
the number of beats/tends to decrease and when the temperature is 16C, the two produce 1 beats/s. The frequency of the fork is :
(a) 50 Hz (b) 75 Hz (c) 100 Hz (d) 150 Hz
19. Two wires of radii r and 2r are welded together end to end. The combination is used as sonometer wire and is kept under tension T. The
welded point is midway between the bridges. The ratio of the number of loops formed in the wires, such that the joint is a node when
stationary vibrations are set up in the wires is (a) 1/4 (b) 1/3 (c) 1/2 (d) 2/3
20. In a kundt’s tube, stationary waves of frequency 1000 Hz are produced. If the distance between 6 successive nodes is 82.5 cm, the speed
of sound in the gas filled in the tube is (a) 300 m/s (b) 330 m/s (c) 360 m/s (d) 390 m/s
21. A wire of density 9  103 kg/m3 is stretched between two clamps 1 m apart and is subjected to an extension of 4.9  10-4 m. If Young’s
modulus of the wire 9  1010 N/m2, The lowest frequency of the transverse vibrations in the wire is :
(a) 35 Hz (b) 70 Hz (c) 105 Hz (d) 140 Hz
22. Two loudspeakers L1 and L2 driven by a common oscillator and amplifier are arranged as shown. The frequency of the oscillator is
gradually increased from zero and the detector at D records a series of maxima and minima. If speed of sound is 330 m/s then the
frequency at which the first maximum is observed is : (a) 165 Hz (b) 330 Hz (c) 495 Hz (d) 660 Hz

1
23. An air column in a pipe, which is closed at one end, will be in resonance with a vibrating fork of frequency 264 Hz if the length of the
column in cm is (velocity of sound is air = 330 m/s) (a) 31.25 (b) 62.50 (c) 93.75 (d) 125
24. A tube closed at one end and containing air produces when excited the fundamental note of frequency 512 Hz. If the tube is open ends
the fundamental frequency that can be excited is (in Hz) (a) 1024 (b) 512 (c) 256 (d) 128
25. A glass tube of 1.0 m length is filled with water. The water can be drained out slowly at the bottom of the tube. If a vibrating tuning fork
of frequency 500 c/s is brought at the upper end of the tube and the velocity of sound is 300 m/s., then the total number of resonances
obtained will be (a) 4 (b) 3 (c) 2 (d) 1
26. When a tuning fork A of unknown frequency is sounded with another tuning fork B of frequency 256 Hz, 3 beats per second are heard.
After that A is loaded with wax and sounded. Again 3 beats per second are heard. The frequency of tuning fork A is :
(a) 250 Hz (b) 253 Hz (c) 259 Hz (d) 262 Hz
27. A wave of frequency 100 Hz is sent along a string towards a fixed end. When this wave travels back then after reflection, anode is
formed at a distance of 10 cm from the fixed end of the string. The speed of the incident wave is :
(a) 40 m/s (b) 20 m/s (c) 10 m/s (d) 5 m/s
28. The lengths of two open organ pipes are 1 and 1 + 1 respectively. Neglecting end correction the frequency of beats between then will
V V Vl Vl
be approximately (V is the speed of sound) (a) (b) (c) (d)
2l 4l 2l 2 l
29. A long glass tube is held vertically in water. A tuning fork is struck and held over the tube. Strong resonances are observed at two
successive lengths 0.50 m and 0.84 m above the surface of water. If the velocity of sound is 340 m/s., then the frequency of the tuning
fork is : (a) 128 Hz (b) 256 Hz (c) 384 Hz (d) 500 Hz
30. Two open organ pipes of lengths 50 cm and 50.4 cm produce 0.3 beats/s. Then the velocity of sound is :
(a) 300 m/s (b) 30 m/s (c) 303 m/s (d) 30.3 m/s
31. An open pipe is suddenly closed at in end with the result that the frequency of third harmonic if the closed pipe is found to be higher by
100 Hz than the fundamental frequency of the open pipe. The fundamental frequency of the open pipe is :
(a) 200 Hz (b) 300 Hz (c) 240 Hz (d) 480 Hz
32. An air column closed at one end and open at the other end, resonates with a tuning fork of frequency v when its length is 45 cm, 99 cm
and at two other lengths in between these values. The wavelengths of sound in the air column
(a) 180 cm (b) 108 cm (c) 54 cm (d) 36 cm

1. A progressive wave of frequency 500 Hz is traveling with a speed of 350 m/s. A compressional maximum appears at a place at a given
instant. The minimum time interval after which a rarefaction maximum occurs at the same point is
(a) 1/250 s (b) 1/500 s (c) 1/1000 s (d) 1/350 s
2. In Q. No. 1 the minimum distance a centre of compression and a centre of rarefaction at any instant is :
(a) 1.4 m (b) 0.70 m (c) 0.35 m (d) 0.175 m
3. A boat at anchor is rocked by waves of velocity 25 m/s. having crests 100 m apart. They reach the boat once every
(a) 4.0 s (b) 8.0 s (c) 2.0 s (d) 0.25 s
4. A progressive wave is represented by the equation y = 0.5 sin (314 t – 12.56 x) when y and x are in metres and t in seconds. Its
wavelength is (a) 0.5 m (b) 1.0 m (c) 1.5 m (d) 2.0 m
5. A wave is expressed by the equation y = 0.5 sin { (0.01 x – 3t)}, where y and x are in metres and t in seconds. The speed of
propagation of the wave is : (a) 100 m/s (b) 150 m/s (c) 200 m/s (d) 300 m/s
6. A wave equation which gives the displacement along the y direction is given by y = 10 -4 sin (60 t + 2x) where x and y are in metres and t
is in seconds. This represents a wave
(a) Travelling with a velocity of 30 m/s in the negative x-direction
(b) of wavelength  metres
(c) of frequency 30/ metres
(d) of amplitude 10-4 m traveling along the negative x-direction
7. Equation of a wave is y = 7 sin (7 t – 0.04  x + /3) where x is in metres and t in seconds. The velocity of the wave is :
(a) 175 m/s (b) 49  m/s (c) 49/ m/s (d) 0.28  m/s
8. A wave of frequency 500 Hz has a velocity 360 m/s. The distance between two nearest points which are 60 out of phase is :
(a) 0.7 cm (b) 12 cm (c) 70 cm (d) 120 cm
9. A transverse progressive wave on a stretched string has a speed of 10 m/s and a frequency of 100 Hz. The phase difference at any instant
between two points on the string which are 2.5 cm apart is (a)  (b) /4 (c) /2 (d) 3/8
10. The equation of a wave is y = 4 sin {/2 (2t + x/8)} where y, x are in cm and time seconds. The amplitude wavelength velocity and
frequency of the wave are respectively (a) 4 cm, 32 cm, 16 cm/s, 0.5 Hz (b) 8 cm, 16 cm, 32 cm/s, 1.0 Hz
(c) 4 cm, 32 cm, 32 cm/s, 0.5 Hz (d) 8 cm, 16 cm, 16 cm/s, 1.0 Hz
11. In Q. 10 the phase difference between two positions of the same particle which are occupied at time interval of 0.4 s is :
(a) 0.2  (b) 0.4  (c) 0.6  (d) 0.8 
12. In Q. 10 the phase difference at any instant two particles 12 cm apart is : (a) /4 (b) /2 (c) 3/4 (d) 
13. Two harmonic waves traveling in the same medium have frequency ratio 1 : 2 and intensity ratio 1 : 36 their amplitude ratio is :
(a) 1 : 3 (b) 8 : 1 (c) 4 : 1 (d) 2 : 1
14. The ratio of the velocities of sound in hydrogen and oxygen at S.T.P. is : (a) 16 : 1 (b) 8 : 1 (c) 4 : 1 (d) 2 : 1

2
15. Two strings A and B made of the same material have equal lengths. The cross-sectional area of A is half that of B while the tension on
A is twice that on B. The ratio of the velocities of transverse waves in A and B is :
(a) 2 : 1 (b) 1 : 2 (c) 2 : 1 (d) 1 : 2
16. When a sound wave of frequency 300 Hz passes through a medium the maximum displacement of a particle of the medium is 0.1 cm.
The maximum velocity of particle is equal to : (a) 60  cm/s (b) 30  cm/s (c) 30 cm/s (d) 60 cm/s
17. A transverse wave is described by the equation y = y0 sin 2 (ft – x/). The maximum particle velocity is equal to four times the wave
velocity if (a)  =  y0/4 (b)  =  y0/2 (c)  =  y0 (d)  = 2  y0
18. If the amplitude of a wave at a distance r from a point source is A the amplitude at a distance 2r will be
(a) 2A (b) A (c) A/2 (d) A/4
19. A wave is represented by the equation y = A sin (10  x + 15 t + /3) where x is in metres and t in second. The expression represents a
wave traveling in the (a) positive x-direction with a speed of 1.5 m/s (b) negative x-direction with a speed of 1.5 m/s
(c) negative x-direction having a wavelength 0.2 m (d) positive x-direction having a wavelength 0.2 m
20. A tuning fork of frequency 90 Hz is sounded and moved towards an observer with a speed equal to one-tenth the speed of sound. The
note heard by the observer will have a frequency (a) 100 (b) 110 (c) 80 (d) 70
21. The difference between the apparent frequencies of a source of sound perceived by a stationary observer during its approach and
recession is 2% of the actual frequency of the source. If the speed of sound is 300 m/s, the speed of the source is :
(a) 12 m/s (b) 6 m/s (c) 1.5 m/s (d) 3 m/s
22. A source of sound is traveling towards a stationary observer. The frequency of sound heard by observer is 25% more than the actual
frequency. If the speed of sound is , that of the source is (a) /5 (b) /4 (c) /3 (d) /2
23. A train is moving at 30 m/s in still air. The frequency of the locomotive whistle is 500 Hz and the speed of sound is 345 m/s. The
apparent wavelengths of sound in front of and behind the locomotive are respectively
(a) 0.63 m, 0.80 m (b) 0.63 m, 0.75 m (c) 0.60 m, 0.85 m (d) 0.60 m, 0.75 m
24. In Q. 23, what would be the apparent wavelengths in front of and behind the locomotive if a wind of speed 10 m/s were blowing in the
same direction as that in which the locomotive is travelling
(a) 0.65 m, 0.73 m (b) 0.60 m, 0.73 m (c) 0.65 m, 0.78 m (d) 0.60 m, 0.71 m
25. A car moving a horn of frequency 1000 Hz is moving directly towards a huge wall at a speed of 15 m/s. If speed of sound is 340 m/s,
then the frequency of the echo heard by the driver is (a) 1046 Hz (b) 954 Hz (c) 1092 Hz (d) 908 Hz
26. A star emits light of wavelength  and it is receding from the earth with a speed 0. The shift in wavelength of the spectral line observed
02 02 0 0
on the earth is : (a)  2
(b)  2
(c)  (d) 
c c c c
27. The frequency of a radar is 780 MHz. When it is reflected from an approaching Aeroplane, the apparent frequency is more than the
actual frequency by 2.6 kHz. The speed of the aeroplane is (a) 0.25 km/s (b) 0.5 km/s (c) 1.0 km/s (d) 2.0 km/s
28. A sample of oxygen at N.T.P. has volume V and a sample of hydrogen at N.T.P. has volume 4 V. Both the gases are mixed and the
mixture is maintained at N.T.P. If the speed of sound in hydrogen at N.T.P. is 1270 m/s, that in the mixture will be
(a) 317 m/s (b) 635 m/s (c) 830 m/s (d) 950 m/s
x 
29. The plane wave is described by the equation y  3 cos   10t  , where x and y are in metres and t in seconds. The maximum
4 2
3
velocity of the particles of the medium due to this wave is : (a) 30 m/s (b) m / s. (c) ¾ m/s (d) 40 m/s
2
30. A source of sound is moving with a constant velocity of 20 m/s emitting a note frequency 1000 Hz. The ratio of the frequencies
observed by a stationary observer while the source is approaching him and after it crosses him is (speed of sound = 340 m/s)
(a) 9 : 8 (b) 8 : 9 (c) 1 : 1 (d) 9 : 10
31. If the pressure amplitude of a sound wave is tripled then the intensity of the wave increases by a factor
(a) 3 (b) 6 (c) 9 (d) 3
32. The extension in a string obeying Hooke’s law is x. The speed of sound in the stretched string is . If the extension in the is increased to
1.5 x, the speed of sound will be : (a) 1.22  (b) 1.61  (c) 1.50  (d) 0.75 