1.WAVES

SRICHAITANYA EDUCATIONAL INSTITUTIONS _NAGOLE _CO

WAVES1. A source moves away from stationary observer with a certain speed v and the ratio of actual to the

apparent frequency as heard by the observer is n. If the two approach each other with the same speed v then the ratio would be

1) 2) 3) *4) 2. Two wires of radii 'r' and 2r are welded together end to end. The combination is stretched and is kept

under a 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

1) 2) *3) 4) 3. An air column is a tube 32 cm long closed at one end in 1 st harmonic is in resonance with a tuning fork.

The air column in another tube open at both ends of length 66cm is in resonance with another tuning fork under fundamental mode. If these two forks are sounded together. They produce 16 beats in 2 seconds.Then the frequencies of forks are1) 250Hz, 258Hz 2) 240Hz, 248Hz 3) 280 Hz, 272Hz *4) 264Hz, 256Hz

4. A uniform rope of mass 100gm and length 4.9m hangs from a rigid support. The time taken by the transverse wave formed in the rope to travel through the full length of the rope is 1) 1.5 sec *2) 1.41 sec 3) 1sec 4) 14.1 sec

5. A pipe of length closed at one end is kept in a chamber of gas of density . A second pipe open at both

ends is placed in a second chamber of gas of density . The compressibility of both the gases is equal if frequency of 1st overtone in both the cases is equal then length of the second pipe is :

1) 2) *3) 4)

6. A column of air at and a tunning fork produce 4 beats per sec when sound together. As the temperature of the air columns is decreased, the number of beats per sec tends to decrease and when the

temperature is the two produce 1beat per sec. Then the frequency of the tuning fork ?

*1) 2) 3) 4) 7. What speed should a galaxy move with respect to us so that the sodium line at wave length 589.0 nm is

observed as 589.66 nm.

1) 208 km/sec *2) 306 km/sec 3) 316 km/sec 4)

8. The equation of a stationary wave is . The wave is formed using a string of length 20cm. The second and 3rd antinodes are located at positions in (cm). 1) 2.5 , 7.5 *2) 7.5 , 12.5 3) 5 , 10 4) 12.5 , 17.5

9. A rod PQ of length ‘L’ is hung from two identical wires A and B. A block of mass M is hung at point R of the rod as shown in figure. The value of ‘x’ so that the 1 st overtone in wire A is in resonance with 3rd

harmonic of B is .


*1) 2) 3) 4)

10. a person is standing between two tuning forks each vibrating at if both the forks move towards right at a speed of 5.5 m/s find the number of beats heard by the person (V=330 m/s)1) 3 2) 6 *3) 8 4) 9

11. Two tuning forks A and B give '4' beats/s. A resonates with a column of air 16cm long closed at one end, and B with a column 32.5cm long open at both ends. Neglecting end correction, the frequencies of A and B are respectively.*1) 260Hz , 256Hz *2) 256Hz , 252Hz 3) 256Hz , 260Hz 4) 252Hz , 256Hz

12. Two identical flutes produces fundamental nodes of frequency 300 Hz at 270C. If the temperature of air

in one flute is increases to 310C the number of the beats per second will be1) 1 *2) 2 3) 3 4) 4

13. A tuning fork of certain frequency produces 4 beats per second with a wire of length 25cm vibrating in its fundamental mode. The beat frequency decreases when the length is slightly shortened. If the length of the wire is shortened by 0.4cm, it produces no beats with the tuning fork. What is the frequency of tuning fork1) 200 Hz 2) 254 Hz *3) 250 Hz 4) 246 Hz

14. The fundamental frequencies of a closed pipe and an open pipe of different lengths are 300 Hz and 400 Hz respectively. If they are joined to form a longer pipe, the fundamental frequency of the long pipe so formed is1) 350 Hz 2) 50 Hz *3) 120 Hz 4) 100 Hz

28. A closed organ pipe and an open organ pipe of same length produce 2 beats per sec when they are set into vibrations simultaneously in the fundamental mode. The length of open pipe is now halved and of closed pipe is doubled, the number of beats produced will be1) 8 *2) 7 3) 4 4) 2

29. The frequency of a stretched uniform wire under tension is in resonance with the fundamental frequency of a closed tube. If the tension in the wire is increased by 8 N, It is in resonance with the first overtone of the closed tube. The initial tension in the wire is*1) 1 N 2) 4 N 3) 8 N 4) 16 N

30. Wavelengths of two notes in air are 80/175 m and 80/173 m. Each note produces 4 beats/s. with a third note of a fixed frequency. The speed of sound in air is1) 400 m/s 2) 300 m/s 3) 280 m/s *4) 320 m/s

31. In order to double the frequency of the fundamental note emitted by a stretched string, the length is reduced 3/4th of the original length and the tension is changed. The factor by which the tension is to be changed is1) 3/8 2) 2/3 3) 8/9 *4) 9/4

32. The path difference between the waves and is


1) *2) 3) 4) 33. An organ pipe P1, closed at one end and vibrating in its first overtone, and another pipe P2 open at both

ends and vibrating in its third overtone, are in resonance with a given tuning fork. The ratio of the length of P1 to that of P2 is

1) *2) 3) 4) 34. Two progressive waves y1=4 sin 400 and y2=3 sin 404 moving in the same direction superpose on

each other producing beats. Then the number of beats per second and the ratio of maxium to minimum intensity of the resultant waves are respectively

1) 2 and 2) 4 and 3) *4) 2 and 35. A tuning fork produces 7 beats/s with a tuning fork of frequency 251 Hz. Unknown fork is now loaded

and 7 beats/s are still heard. The frequency of unkown fork was1) 241 Hz 2) 244 Hz *3) 258 Hz 4) 266 Hz

36. 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 330 m/s, then the total number of resonances obtained will be 1) 4 *2) 3 3) 2 4) 1

37. The string of a sonometer is divided into two parts with the help of a wedge. The total length of the string is 1m and the two parts differ by 2mm. When sounded together they produced two beats per second. The frequencies of the notes emitted by the two parts are1) 4999 & 497 Hz *2) 501 & 499 Hz 3) 501 & 503 Hz 4) None

38. When a train is approaching the stationary observer, the apparent frequency of the whistle observed as 100 Hz, while when it has passed away from the observer with same speed, it is 50 Hz. Calculate the frequency of the whistle when the observer moves with the train (V=330m/s)1) 33.3 Hz 2) 50 Hz *3) 66.6 Hz 4) 75 Hz

39. A car travelling at a speed of 54 km/hr towards a large wall horns a sound of frequency 400 Hz if the person stands behind the car such that the car receding from him approaches the wall the difference in frequencies of the two sounds one recieved directly from the car and the other reflected from the wall (speed of sound is 335 m/s)*1) 35.9 Hz 2) 20 Hz 3) 70 Hz 4) 30 Hz

40. An open organ pipe of length L vibrates in its fundamental mode. The pressure variation is maximum 1) At the two ends *2) at the middle of the pipe3) At distances L/4 inside the ends 4) At distances L/8 inside the ends

41. End correction in the closed pipe of resonating air column apparatus is 1 cm. If the first resonating length 16 cm then the second resonating length is obtained at 1) 48 cm *2) 50 cm 3) 51 cm 4) 52 cm

42. When two waves of nearly equal frequencies super impose then the frequency of combined wave is

that of amplitude is and the beat frequency is Arrange them in an order

1) *2) 3) 4)


43. An open pipe 20 cm long resonates, when filled with oxygen, with a given tuning fork. what is the length of an open pipe filled with hydrogen which will be in resonance with the same tuning fork?

Given:velocity of sound in oxygen = 320 ms-1 and velocity of sound in hydrogen = 1280 ms-1.*1) 80 cm 2) 40 cm 3) 20 cm 4) 60 cm

44. An open organ pipe of length l is sounded together with another open organ pipe of length l+x in the fundamental tones. Speed of sound in air is v. The beat frequency heard will be (x<<l)

1) 2) *3) 4) 45. A string oscillating at fundamental frequency under a tension of 225N produces 6 beats per second with a

sonometer. If the tension is 256N, again oscillating at fundamental note it produces 6 beats per second with the same sonometer. What is the frequency of the sonometer?1) 256 2) 255 3) 280 *4) 186

46. The amplitude of a damped oscillator decreases to 0.25 times its original magnitude in 4 sec. In another 4 sec it will decrease to x times it original magnitude. Where x equals 1) 0.05 *2) 0.0625 3) 0.625 4) 0.00625

47. A travelling wave in a string has speed 5 cm/s in –ve x direction its amplitude is 10 mm and wavelength

1m. At a particular time a point P has displacement mm. Find the velocity vector of point P

*1) 2) 3) 4) 48. An open pipe resonates to a frequency 'f1' and a closed pipe resonates to a frequency 'f2'. If they are

joined together to form a longer tube, then it will resonate to a frequency of (Neglect end corrections)

1) 2) 3) *4) 49. The driver of a car moving towards a vertical wall notices that the frequency of his car’s horn changes

from 440 Hz to 480Hz. The speed of the car if that of the sound is 345m/s*1) 15 m/s 2) 30 m/s 3) 45 m/s 4) 60 m/s

50. (A) : According to Laplace the propagation of sound in air is an adiabatic process.(B) : Pressure has no effect on velocity of sound in a gas as long as temperature remains constant.

(C) : The velocity of sound in air changes by 0.61 m/s when temperature changes by 10C.*1) All are true 2) A , B are only true 3) B are true 4) A , C are only true

51. The length of the tube of a microscope is 10 cm. The focal lengths of the objective and eye lenses are 0.5 cm and 1.0 cm. The magnifying power of the microscope is about1) 5 2) 23 3) 166 *4) 500

52. A vehicle sounding a whistle of frequency 256Hz is moving on a straight road, towards a hill with a velocity of 10 m/s. The number of beats produced per second is (Velocity of sound 330 m/s)1) zero 2) 10 3) 14

*4) 16


53. A source of sound and an observer are approaching each other with the same speed, which is equal to

times the speed of sound. The apparent relative change in frequency of source is *1) 22.2 % increases 2) 22.2 % decreases 3) 18.2 % decreases 4) 18.2 increases

54. A source producing sound of frequency 170 Hz is approaching a stationary observer with a velocity 17 m/s. The apparent change in the wavelength of sound heard by the observer (speed of sound in air = 340 m/s)*1) 0.1 m 2) 0.2 m 3) 0.4 m 4) 0.5 m

55. A radar sends a radio signal of frequency Hz towards an aircraft approaching the radar. If the

reflected wave shows a frequency shift of Hz the speed with which the aircraft is approaching the

radar in m/s (velocity of radar signal is m/s)1) 150 2) 100 *3) 50 4) 25

56. A Whistle of frequency 540 Hz rotates in a horizontal circle of radius 2m at an angular speed of 15 rad/sec. The highest frequency heard by a listener at rest with respect to centre of circle (velocity of sound in air is 330 m/s)1) 509 Hz *2) 594 Hz 3) 598 Hz 4) 602 Hz

57. An observer is standing 500 m away from a vertical hill, starting between the observer and the hill, a police van sounding a siren of frequency 1000 Hz moves towards the hill with a uniform speed. If the frequency of the sound heard directly from the siren is 970 Hy, the frequency of the sound heard after reflection from the hill (in Hz) is about (velocity of sound = 330 m/s)1) 1042 *2) 1032 3) 1022 4) 1012

58. A source of sound producing wavelength 50 cm is moving away from a stationary observer with of speed of sound. Then what is the wavelength of the sound heard by the observer.*1) 60 cm 2) 70 cm 3) 55 cm 4) 40 cm

59. A car with a horn of frequency 620 Hz travels towards a large wall at a speed of 20 m/s. The frequency of echo of sound as heard by the driver is (velocity of sound = 330 m/s)*1) 700 Hz 2) 660 Hz 3) 620 Hz 4) 580 Hz

60. A person going away from a factory on his scooter at a speed of 36 kmph listens to the siren of the factory. If the frequency of the siren is 660 Hz and a wind is blowing opposite to the direction of motion of scooter at 36 kmph. The frequency heard by the person is (velocity of sound is 340 m/s)*1) 640 Hz 2) 600 Hz 3) 510 Hz 4) 650 Hz

61. An observer is moving with a velocity of 50 m/s from a source of sound of frequency 100 Hz. If speed of sound in air is 333 m/s the observed frequency is*1) 85 Hz 2) 91 Hz 3) 100 Hz 4) 149 Hz

62. When both source and listener move in the same direction with a velocity equal to half the velocity of sound, the change in frequency of the sound as dected by the listener is (frequency of sound n )

*1) zero 2) n 3) 4)


63. An observer moves towards a stationary source of sound with a speed of the speed of sound. The

wavelength and frequency of the source emitted are and f respectively. The apparent frequency and wavelength recorded by the observer are

*1) 1.2f and 2) f and 3) 0.8f and 4) 1.2f and 64. A whistle emitting a sound of frequency 440Hz is tied to a string of 1.5m length and rotated with an

angular velocity of 20rad/s in the horizontal plane. Then the range of frequencies heard by an observer stationed at a large distance from the whistle will be (v=330m/s)1) 400.0Hz to 500.0Hz2) 403.3Hz to 580.0Hz 3) 420.0Hz to 480.0Hz *4) 403.3Hz to 484.0Hz

65. The apparent frequency of the whistle of an engine becomes in the ratio of 6:5 as the engine passes a stationary observer. If the velocity of sound is 330m/s, then the velocity of the engine is1) 3m/s *2) 30m/s 3) 0.33m/s 4) 660m/s

66. Two cars are moving on two perpendicular roads towards a crossing with uniform speeds of 72km/hr and 36km/hr. If first car blows horn of freqency 280Hz, then the frequency of horn heardby the driver of

second car when the line joining the cars makes angle of 450 with the roads, will be1) 321Hz *2) 298Hz 3) 389 Hz 4) 200Hz

67. A source emitting a sound of freqency f is placed at large distance from an observer. The source starts moving towards the observer with a uniform acceleration 'a'. The frequency heard by the observer corresponding to the wave emitted just after the source starts is.., (The speed of sound in medium is v.)

1) 2) 3) *4) 68. A source of sound of frequency 256Hz is moving rapidly towards a wall with a velocity of 5m/s. If sound

travels at a speed of 30m/s, then number of beats per second heard by an observer between the wall and the source is1) 7.7Hz 2) 9Hz 3) 4Hz *4) none of these

69. The driver of a car approaching a vertical wall notices that the frequency of the horn of his car changes from 400Hz to 450Hz after being reflected from the wall. Assuming speed of sound to be 340m/s, the speed of approach of car towards the wall is1) 10m/s *2) 20m/s 3) 30m/s 4) 40m/s

70. If the source is moving towards right, wavefront of sound waves get modified to

1) *2) 3) 4) None of these

71. A wave y = a sin (wt-kx) on a string meets with another wave producing a node at x=0. The equation of the unknown wave is 1) y = a sin (wt+kx) 2) y=a cos (kx-wt) 3) y=-a cos (kx-wt) *4) y=- a sin (kx+wt)

72. A wave represented by the given equation y=a cos (wt+kx) super impose on anther wave giving a stationary wave having node at x=0 what is the other wave. 1) y=a cos (wr+kx) 2) y=a cos (wt-kx) *3) y=-a cos (wt-kx) 4) y=-a sin (wt + kx)

73. The ratio of densities of nitrogen and oxygen is 14:16. The temperature at which the speed of sound in nitrogen will be same as that in oxygen at 550C is


1) 2) 3) *4) 74. A sample of oxygen at NTP has volume V and a sample of hydrogen at NTP has the volume 4V. Both

the gases are mixed. If the speed of sound in hydrogen at NTP is 1270 m/s. that in mixture is 1) 317 m/s *2) 635 m/s 3) 830 m/s 4) 950 m/s

Comprehension (20 – 21)

The displacement of the medium in a sound wave is given by where A, a and b are positive constants. The wave is reflected by an obstacle situated at x = 0. The intensity of the reflected wave is 0.64 times that of the incident wave.

75. The wavelength and frequency of the incident wave respectively are

1) 2) 3) *4) 76. The equation for the reflected wave is

*1) 2)

3) 4) 77. Assertion (A) : With increase in humidity velocity of sound in air increases.

Reason (R) : With increase in humidity, density of air decreases*1) Both A and R are correct and R is correct explanation of A2) Both A and R are correct, but R is not correct explanation of A.3) A is True but R is false 4) A is false but R is true

78. Laplace’s correction in the formula for the speed of sound given by Newton was needed because sound waves1) are longitudinal 2) propagate isothermally

*3) propagate adiabatically 4) have long wavelengths 79. A sound tone is produced under water. When is enters air

1) its frequency and wavelength increase 2) its frequency and wavelength decrease*3) wave length decreases and frequency does not change4) wave length increases and frequency does not change

80 . A sound wave travelling along an air column of a pipe gets reflected at the open end of the pipe. What is the phase difference between the incident and reflected waves at the open end ?

1) 2) *3) 4)

81. Two waves of same frequency and intensity superimpose with each other in opposite phases, then after

superimposition the

1) intensity increases by 4 times 2) intensity increases by two times

3) frequency increases by 4 times *4) none of these

82. Which two of the given transverse waves will give stationary waves when get superimposed

(A) (B) (C)

*1) A and B 2) A and C 3) B and C 4) any two

83. Assertion (A) : The change in air pressure effect the speed of sound Reason (R) : The speed of sound in a gas is proportional to square root of pressure1) Both A and R are correct and R is correct explanation of A2) Both A and R are correct, but R is not correct explanation of A.


3) A is True but R is false *4) A is false but R is true

84. What must be the velocity of star, if the spectral line nm of a star shifts by 0.1 towards longer wavelength from the position of the same line in terrestrial laboratory? (Assume the shift to be due to Doppler effect)1) 6 x 103 m/s *2) 5 x 103 m/s 3) 0.5 x 103 m/s 4) 6.25 x 103 m/s

85. Two particles of medium disturbed by the wave propagation are at x1 = 0 and x2 = 1 cm. The respective displacements (in cm) of the particles can be given by the equations y 1 = 2 Sin 3t, y2 = Sin (3t - /8). The wave velocity is 1) 16 cm/s *2) 24 cm/s 3) 12 cm/s 4) 8 cm/s

86. Consider a wave represented by y = a Cos2 (t – kx) where symbols have their usual meanings. This wave has 1) an amplitude a, frequency , and wavelength 2) an amplitude a, frequency 2, and wavelength 2 *3) an amplitude a/2, frequency 2, and wavelength /2

4) an amplitude a/2, frequency 2, and wavelength 87. A man is watching two trains, one leaving and the other coming in with equal speed of 4 m/s. If they

sound their whistles, each of frequency 240 Hz, the number of beats heard by the man (velocity of sound in air is 320 m/s) will be equal to *1) 6 2) 3 3) 0 4) 12

88. The equation of a stationary wave is where x is in cm and t is in s. The separation between consecutive nodes will be *1) 20 cm 2) 10 cm 3) 40 cm 4) 30 cm

89. Two tuning forks A and B give 4 beats/s when sounded together. The frequency of A is 320 Hz. When some wax is added to B and it is sounded with A, 4 beats/s per second are again heard. The frequency of the tuning fork A will be 1) 312 Hz 2) 316 Hz *3) 324 Hz 4) 328 Hz

90. Two organ pipes, both closed at one end, have lengths and . Neglect end correction. If the velocity of sound in air is V, then the number of beats /s is

1) 2) *3) 4) 91. An organ pipe A closed at one end vibrating in its fundamental frequency and another pipe B open at both

ends is vibrating in its second overtone are in resonance with a given tuning fork. The ratio of length of pipe A to that of B is 1) 1 : 2 2) 3 : 8 3) 2 : 3 *4) 1 : 6

92. A stretched wire of some length under a tension is vibrating with its fundamental frequency. Its length is decreased by 45% and tension is increased by 21%. Now fundamental frequency 1) increases by 50% *2) increases by 100% 3) decreases by 50% 4) decreases by 25%

93. There is a set of four tuning forks, one with the lowest frequency vibrating at 550 Hz. By using any two tuning forks at a time, the following beat frequencies are heard : 1, 2, 3, 5, 7, 8. The possible frequencies of the other three forks are 1) 552, 553, 560 2) 557, 558, 560 3) 552, 553, 558 *4) 551, 553, 558

94. A wave represented by the equation y = a Cos (kx – t) is superposed with another wave to form a stationary wave such that the point x = 0 is a node. The equation for the other wave is


1) a Sin (kx + t) 2) – a Cos (kx – t) *3) –a Cos (kx + t) 4) – a Sin (kx – t) 95. The displacement vibration of string of length 60 cm fixed at both ends are represented by

nodes are located at distances…. Cm excluding the ends of string *1) 20, 40 2) 15, 45 3) 15, 40 4) 20, 45

96. The stationary wave in closed organ pipe is the result of the superposition of

and

1) 2)

3) *4)

97. Two waves of equal amplitude and equal frequency travel in the same direction in a medium. The amplitude of the resultant wave is

1) 0 2) *3) 4) between 0 and 98. The speed of transverse waves in a stretched string is 700 cm/sec. If the string is 2m long, the frequency

with which it resonates in fundamental mode is

1) *2) 3) 4) 99. In an experiment, the string vibrates in 4 loops when 50 gm wt is placed in pan of weight 15gm. To make

the string vibrate in 6 loops the weight that has to be removed from the pan is approximately1) 72 gm *2) 36 gm 3) 21 gm 4) 29 gm

100. The tension of a stretched string is increased by 69% in order to keep its frequency of vibration constant, is length must be increased by

*1) 30% 2) 20% 3) 69% 4)

101. A wire under a load has a frequency . When the load is completely immersed in water, its frequency is

the relative density of the material of the load is

*1) 2) 3) 4)

102. The equation of a stationary wave in a string under tension T along x-direction from to 1, will be

*1) 2)

3) 4)

103. A string is rigidly tied at two ends and its equation of vibration is given by then minimum length of string is

1) 1m *2) 3) 5m 4) 104. The difference between frequencies of successive overtones of a sonometer wire is 150 Hz. The

frequency of its first overtone is 1) 150 Hz 2) 200 Hz 3) 250 Hz *4) 300 Hz


105. A sonometer wire vibrates with a frequency of 500 Hz when the tension is and with a frequency of

400 Hz when the tension is . Its frequency of vibration for a tension is (in Hz)1) 450 *2) 300 3) 100 4) 210

106. A sonometer wire of length carries as block of mass M and density ‘d’ at the other end. If the block is immersed in a liquid of density , the fundamental frequency decreases to a factor of

1) *2)

3) 4) 107. The equation of the standing wave in string clamped at both ends, vibrating in its third harmonic is given

by , where, x and y are in cm and t in sec.a) The frequency of vibration is 300 Hzb) The length of the string is 30 cm

c) The nodes are located at 1) a, b 2) a, c 3) b, c *4) a, b, c

108. If Young’s modules of the material of a rod is and density is the time taken by a sound wave to travel through 2m of the rod is

1) 2) *3) 4) 109. The tones that are separated by three octaves have a frequency ratio

1) 6 2) 3 3) 16 *4) 8110. If the temperature is raised by 1K from 300K then the percentage charge in the speed of sound in the

gaseous mixture is *1) 0.167% 2) 2% 3) 1% 4) 0.334%

111. A string of length l between two bridges of a sonometer vibrates in first overtone. The amplitude of vibration is maximum at

*1) 2) 3) 4) cannot say112. A sonometer is set on the floor of a lift. When the lift is at rest, the sonometer wire vibrates with

fundamental frequency 256 Hz. When the lift goes up with acceleration , the frequency of vibration of the same wire changes to

1) 512 Hz *2) 320 Hz 3) 256 Hz 4) 204 Hz

113. A standing wave having 3 nodes and 2 antinodes is formed between two atoms having a distance between then the wavelength of the standing wave is

*1) 2) 3) 4) 114. In a stationary wave along a string the strain is

1) Zero at the antinodes 2) Maximum at the antinodes3) Zero at the nodes *4) Maximum at the nodes

115. In a stationary wave represented by , amplitude of the component progressive wave is


*1) 2) 3) 4)

116. The elevation of a cloud is above the horizon. A thunder is heard 8 s after the observation of

lighting. The speed of sound is . The vertical height of cloud form ground is

1) 2826 m 2) 2682 m *3) 2286 m 4) 2068 m117. The ratio of speed of sound in neon to that in water vapours at any temperature (when molecular weight

of neon is and for water vapours is )*1) 1.06 2) 1.60 3) 6.10 4) 15.2

118. The bulk modulus and the density of water are greater than those of air. With this much of information we can say that velocity of sound in air

1) Is larger than its value in water 2) Is smaller than its value in water 3) Is equal to its value in water *4) Cannot be compared with its value in water

119. A wave pulse on a string has the dimension shown in figure. The wave speed is . If point O is

a free end. The shape of wave at time is

1) 2)

3) *4)

120. Equations of a stationary and a travelling waves are as follows and

The phase difference between two points and are and

respectively for the two waves. The ratio is


1) 1 2) 3) *4)

121. The time taken by sound waves to travel the distance if the air temperature between them varies

linearly from to (velocity of sound in air is given by

*1) 2) 3) 4) 122. A standing wave is maintained in a homogeneous string of cross-sectional area “s” and density . It is

formed by the superposition of two waves travelling in opposite directions given by the equation

and The total mechanical energy confined between the sections corresponding to the adjacent antinodes is

1) 2) *3) 4) 123. Two waves are represented by

The intensity ratio of the two waves is

1) 2) 3) *4)

124. The vibration of a stretched string fixed at both ends are described by .The minimum length of the wire will be

1) 1m *2) 0.5 m 3) 5 m 4) 125. The equation for the vibration of a string fixed at both ends vibrating in its third harmonic is given by

The length of the string is1) 24.6 cm 2) 12.5 cm 3) 20.6 cm *4) 15.7 cm

126. A string is under tension so that its length is increased by times its original length. The ratio of fundamental frequency of longitudinal vibrations and transverse vibrations will be:

1) 2) *3) 4)

127. A tuning fork produces a wave of wavelength 110 cm in air at . The wavelength at would be 1) 110 cm *2) 115 cm 3) 120 cm 4) 130 cm

128. The speed of sound in a mixture of 1 mol. Of Helium and 2 mol. Of oxygen at 300K is 1) 300 m/s *2) 400 m/s 3) 500 m/s 4) None of these

129. A standing wave is produced on a string clamped at one end and free at the other. The length of the string

*1) Must be an integral multiple of 2) Must be an integral multiple of

3) Must be an integral multiple of 4) May be an integral multiple of

130. 25 tuning forks are arranged in series in the order of decreasing frequency. Any two successive forks produces 3 beats/s. If the frequency of the first tuning fork is the octave of the last fork, then the frequency of the 21st fork is


1) 72 Hz 2) 288 Hz *3) 84 Hz 4) 87 Hz131. A police car moving at 22m/s chases a motorcyclist. The policeman sounds his horn at 176Hz, while

both of them move towards a stationary siren of frequency 165Hz.Calculate the speed of the motorcycle, If it is given that the motorcyclist does not observe any beats (Velocity of sound=330m/s)1) 33 m/s *2) 22 m/s 3) Zero 4) 11 m/s

132. An open pipe of length 'l' vibrates in fundamental mode. The pressure variation is maximum at

1) from ends *2) the middle of the pipe

3) the ends of pipe 4) at from ends of pipe133. Two vibrating strings of the same material but length L and 2L have radii 2r and r respectively. They are

stretched under the same tension. Both the strings vibrate in their fundamental modes, the one of length

L with frequency and the other with frequency . The ratio is given by 1) 2 2) 4 3) 8 *4) 1

134. A wave disturbance in a medium is described by where x and y are in meter and t is in second, Then wrong statement is

1) A node occurs at 2) an antinode occurs at

3) The speed of wave is *4) The wavelength of wave is 0.3 m135. The extension in a string, obeying Hooke’s law, is . The speed of transverse wave in the stretched string

is v. if the extension in the string is increased to 1.5x, the speed of wave will be

*1) 1.22 v 2) 3) 4)

136. The equation represents a wave with:

1) amplitude a, frequency n and wavelength

2) amplitude a, frequency 2n and wavelength 2

3) amplitude a/2, frequency 2n and wavelength

*4) amplitude a/2, frequency 2 n and wavelength /2

137. The figure shows four progressive waves A, B, C & D. It can be concluded from the figure that with respect to wave A:

1) The wave C is ahead by a phase angle of the wave B lags behind by a phase angle


*2) The wave C is lags behind by a phase angle of the wave B is ahead by a phase angle

3) The wave C is ahead by a phase angle of the wave B lags behind by a phase angle .

4) The wave C is lags behind by a phase angle of the wave B lags behind by a phase angle .138. What is the percentage change in the tension necessary in a sonometer of fixed length to produce a note

one octave lower (half of original frequency) than before 1) 25% 2) 50 % 3) 67% *4) 75%139. A chord attached about an end to a vibrating fork divides it into 6 loops, when its tension is 36 N. The

tension at which it will vibrate in 4 loops is:

1) 2) 3) *4) 81 N140. Two vibrating strings of same length, same cross section area and stretched to same tension are made of

materials with densities . Each string is fixed at both ends. If represents the frequency of

fundamental mode of vibration of the one made with density and for another, then is

1) 2) 2 *3) 4) 141. A string of length L is clamped at each end and vibrates in a standing wave pattern. The wavelengths of

constituent traveling waves can not be *1) 3L 2) 2L 3) 2L/3 4) L/2

142. A mass less rod of length L is suspended by two identical strings AB and CD of equal length. A block of mass m is suspended from point O such that BO is equal to ‘x’. Further it is observed that the frequency of 1st harmonic in AB is equal to 2nd harmonic frequency in CD. ‘x’ is

*1) 2) 3) 4) 143. An object of specific gravity is hung from a thin steel wire. The fundamental frequency for transverse

standing waves in the wire is 300 Hz. The object is immersed in water so that one half of its volume is submerged. The new fundamental frequency in Hz is.

*1) 2) 3) 4)

144. The ends of stretched wire of length L are fixed at x = 0 and In one experiment, the displacement

of the wire is and energy is and in another experiment its displacement is

and energy is then


1) 2) *3) 4) 145. A stretched wire resonates with a given tuning fork forming standing waves with five antinodes between

the two bridges when a mass of 9 kg is suspended from the wire. When this mass is replaced by a mass M, the wire resonates with the same tuning fork forming three antinodes for the same positions of the bridges. The value of M is

*1 ) 25 kg 2) 5 kg 3) 12.5 kg 4) 1/25 kg

146. Equation of a stationary and a traveling waves are as a follows and

.

The phase difference between two points X1 and x2 is in the standing wave (y1) and is in

travelling wave (y2) then ratio is 1) 1 2)5/6 3)3/4

*4)6/7147. A uniform rope having mass m hangs vertically from a rigid support. A transverse wave pulse is

produced at the lower end. The speed u of wave pulse varies with height h from the lower end as: 1) 2)

*3) 4)

148. The mass of 1 mole of air is 29 x 10-3 kg, then speed of sound in air at standard temperature and pressure is*1) 331.3 m/s 2) 280 m/s 3) 310 m/s 4) 320 m/s

149. Two sitar strings A and B playing the note ‘Dha’ are slightly out of tune and produce beats of frequency 6 Hz. The tension of the string B is slightly increased and the beat frequency is found to decrease to 3 Hz. If frequency of A is 428 Hz, then original frequency of B is1) 434 Hz *2) 422 Hz 3) 425 Hz 4) 431 Hz

150. The wrong statement in the following pertaining to stationary wave1) All the particles except at nodes vibrate with different amplitude but same frequency as that of component wave2) The phase difference between the particles in the successive loops is .3) The phase difference between any two particles in same loop is zero

*4) At nodes the strain is zero151. A Transverse wave equation by y =y0 sin 2π(t/T - x/ג) . if maximum particle velocity is equal to 4 times

the wave velocity them wave length is


1) πy°/3 2) πy°/4 3 πy°/5 *4) πy°/2

152. The amplitude of a wave is represented by . Then resonance will occur when1) a = 0, b = c 2) b = 0, a = c 3) b + a = c *4) all the above

153. A : A person hears maximum sound at displacement anti node (or) pressure nodeB : Quality of sound from one open organ pipe is different than from a closed pipe of same frequencyC : Two organ pipes of same length open at both ends produce sound of different pitch if their radii are differentD: If oil of density higher than water is filled in place of water, in a resonance tube, its frequency remain unchanged*1) All are true 2) A, B are only true 3) B,C,D are true 4) A, C are only true

154. The equation of a stationary wave is y = 0.9 Cos Sin(200 t) where x is in cm and t is in seconds. The separation between consecutive nodes is1) 10 cm *2) 20 cm 3) 30 cm 4) 40 cm

155. The length of a sonometer wire AB is 100 cm. Where should the two bridges be placed from A to divide the wire in 3 segments whose fundamental frequencies are in the ratio of 1 : 2 : 61) 30 cm, 90 cm *2) 60 cm, 90 cm 3) 40 cm, 80 cm 4) 20 cm, 30 cm

156. A wire whose linear density is 5 x 10-3 kg/m is stretched between two points with a tension 450 N. The wire resonates at a frequency of 420 Hz. The next higher frequency at which the same wire resonates is 490 Hz. What is the length of the wire? 1) 1.2 m 2) 1.8 m *3) 2.1 m 4) 8.1 m

157. The ratio of the speed of the sound in nitrogen gas to that in helium gas, at 300 K is

1) 2) *3) 4) 158. A cylindrical tube, open at both ends, has a fundamental frequency fo in air. The tube is dipped vertically

into water such that half of its length is inside water. The fundamental frequency of the air column now is

1) *2) 3) 4) 2159. An open organ pipe and closed pipe have same length. The ratio of frequencies of their nth over tone is

1) *2) 3) 4) 160. Two progressive waves y1 = 4 sin 400 t and y2 = 3 sin 404 t moving in the same direction superpose

on each other producing beats. Then the number of beats per second and the ratio of maximum to minimum intensity of the resultant waves are respectively1) 2 and 5/1 2) 4 and 49/1 3) 4 and 16/9 *4) 2 and 49/1

161. 64 tuning forks are arranged such that each fork produces 4 beats per second with next one. If the frequency of the last fork is octave of the first, the frequency of 16th fork is1) 316 Hz 2) 322 Hz *3) 312 Hz 4) 308 Hz


162. Two tuning forks A and B vibrating simultaneously produce 5 beats/s. Frequency of B is 512 Hz. If one arm of A is filed, the number of beats per second increases. Frequency of A is1) 502 Hz 2) 507 Hz *3) 517 Hz 4) 522 Hz

163. The equation for the vibration of a string fixed at both ends vibrating in its third harmonic is given by y = 2sin (0.6x) Cos(500 t), y and x in cm. Then length of the string is1) 12.5 cm 2) 24.6 cm *3) 15.7 cm 4) 20.6 cm

164. A string is under tension so that its length is increased by 1/x times it original length. The ratio of fundamental frequency of longitudinal vibrations and transverse vibrations will be

1) x : 1 *2) : 1 3) 4) 1 :

165. A standing wave is maintained in a homogenous string of cross sectional area A and density . Its formed by the superposition of two waves travelling in opposite direction given by the equations

Total mechanical energy confined between the sections corresponding to the adjacent anti node is

*1) 2) 3) 4) 166. First overtone frequency of a closed pipe is equal to the first overtone frequency of an open organ pipe.

Further nth harmonic of closed organ pipe is also equal to the mth harmonic of open pipe, where n and m are1) 5, 4 *2) 9, 6 3) 7, 5 4) 7, 3

167. For certain organ pipe three successive resonance frequencies are observed at 425 Hz, 595 Hz and 765 Hz respectively. If the speed of sound in air is 340 m/s, then the length of the pipe is1) 0.2 m 2) 0.4 m 3) 2 m *4) 1 m