Sound Waves Questions and Answers

Two tuning fork having frequency 320 Hz 324 Hz produce beat phenomena Determine a Beat time period b Minimum time interval in which maximum intensity become minimum c Number of beat per three seconds rodriven by the same amplifier system A perso

4 A source of sound gives 5 beats per second when sounded with another source of frequency 100 Hz The second harmonic of the source together with a source of frequency 205 Hz gives 5 beats per second What is the frequency of the source a 105 Hz c 95 Hz b 205 Hz d 100 Hz

The fundamental frequency in an open organ pip is equal to the third harmonic of a closed organ pipe If the length of the closed organ pipe is 20 cm th length of the open organ pipe is 2 8 cm 4 16 cm 1 13 2 cm 3 12 5 cm

The figure shows an instantaneous profile of a tope carrying a progressive wave moving from left to VIAW right then A B a the phase at A is greater than the phase at B b the phase at B is greater than the phase at A c A is moving upwards el B is moving upwards 1 a c 3 b c 2 a d 4 b d The 1 2 3 4 29 If t 30

Length of a sonometer wire stretched between two points is 105 cm Two bridges are kept between two ends so that sonometer wire is divided into three parts whose fundamental frequencies are in ratio of 1 5 15 The lengths of three parts are 1 5 cm 20 cm 80 cm 2 20 cm 35 cm 50 cm 3 25 cm 35 cm 45 cm 4 75 cm 25 cm 5 cm

A sound source is moving on a circular path of radius R with constant angular speed o in anticlockwise direction and emits a frequency n An observer performs simple harmonic along the path QPR with time 2 period T as shown in the figure If at t 0 source is at A and observer is at Q and assume OP is very large as compare to radius R and QP then B 0 Q P R

Sound Wave Q20 A person standing at a distance of 6 m from a source of sound receives sound wave in two ways one directly from the source and other after reflection from a rigid boundary as shown in the figure The maximum wavelength for which the person will receive maximum sound intensity is A 4 m B 16 III 4m C 2 m 6 E

8 Two sound sources of frequency 360 Hz each one moving toward observer while second moving away from observer with same speed 5 5 m s then number of beats produced per second is v 330 m s 1 2 3 12 2 18 4 25

A train is moving in an elliptical orbit in clockwise sense with speed 90 m s The elliptical orbit is 1 1250 Hz represented by the equation driver gives a whistle of 1800 Hz at A which is received by guard at B The frequency received by the guard is speed of sound is 340 m s A 0 O x 5 y 1 The 16 9 B 2 1300 Hz

An organ pipe of 3 9 m long open at both ends is driven to third harmonic standing wave If the amplitude of pressure oscillation is 1 of mean atmospheric pressure Po 10 N m The maximum displacement of particle from mean position will be Given velocity of sound 300 m s and density of air 1 3kg m in mm to nearest integer

A radio wave of intensity is reflected by a surfac Find intensity if pressure exerted on the surface 2x10 8 N m a 3 N m b 4 N m c 6 N m d 7 N m

01 Two tuning forks of frequencies 100 Hz and 106 Hz are sounded together What is the time interval between a waxing and the nearest waning a 1 2 2 S c S 3 b d 10 10 S S

If sound wave travelling through air is reflected from a wall then the phase difference between incident and reflected pressure wave will be 1 Zero 3 si 2 mumining 4 T IN 5 mx

10 2 A square ground of side has a circular running track of radius 14 The centre of square ground coincides with the centre of circular track A man is running on the circular track the angular velocities of line joining man to centre of the circle is 22 rad s while a car is running on adjacent road as shown The car moves in such a way that the car man and centre lie on a straight line always A source of sound is kept at the centre of circular track The frequency of sound produced by source is 300 Hz The velocities of sound in air is 330 m s Now answer the following questions width of the track is ignorable 53 E14 If at any time t line joining man to centre of the track makes angle 9 with y axis Find the value of e at which an observer in the car observes minimum frequency A 30 C 60 B 45 D 37

The time of reverberation of a room A is one second What will be the time in seconds of reverberation of a room having all the dimensions double of those AIPMT Prelims 2006 of room A 1 2 2 4 1 2 3 4 1

Two tuning forks have frequencies 520 Hz a 524 Hz respectively On sounding these for together the time interval between two successi maximum intensity is 1 2 1 2 S 3 1 s 2 S 4 4 2 S

agation is 2 cm s The wavelengths of 60 cm and 61 cm produce 9 beats second The velocity of sound approximately 1 330 m s 3 340 m s 2 335 m s 4 325 m s

1 The third overtone of an open organ pipe is in resonance with the second overtone of a closed organ pipe If the length of the open pipe is 8 cm then the length of the closed pipe is a 10 cm b 8 cm c 12 cm d 5 cm

The maximum possible sound level in dB of sound wave in air will be nearly density of air 1 3 kg m speed of sound 390 m s and atmospheric pressure 1 01 105 N m 1 90 dB 2 80 dB 3 190 dB 4 180 dB IXA In a

D A pipe closed at one end and open at the other end resonates with sound waves of frequency 135 Hz and also 165 Hz but not with any wave of frequency intermediate between these two Then the frequency of the fundamental note is a 30 Hz c 60 Hz b 15 Hz d 7 5 Hz 2

the length of tube Given below are some functions of x and t to represent the displacement transverse or longitudinal of a I elastic wave State which of these represent i a travelling wave ii a stationary wave or iii none at all y 2 x vt y cosx sint cos2xsin2t a y cos 3x sin 10t y 3 sin 5x 0 5t 4 cos 5x 0 5t HOO 10 an pipe are 1944 and 2592 Hz b d 60

Example 2 The equation of a sound wave in air is given by p 0 01 N m sin 1000 s t 3 0 m x a Find the frequency wavelength and the speed of sound wave in air b If the equilibrium pressure of air is 1 0 x 10 N m what are the maximum and minimum pressures at a point as the wave passes through that point

34 In a long cy adjusted and the air column above it is made to vibrate in unison with a vibrating tuning fork kept at the open end Maximum sound is heard when the air column lengths are equal to 32 1 4 2 4 2 1 1 1 2 3 5 4 3 540 3 22 2 4 32 52 4 4 4

In an experiment sonometer wire vibrates in 4 loops when a 50 g weight is placed in the pan of weight 15 g To make the wire vibrates in 6 loops the mass that has to be removed from the pan is approximately frequency of vibration remains constant 1 12 g 2 24 g

The sound level of a dog s bark is 50 dB The intensity of a rock concert is 10 000 times that of dog s bark What is the sound level of the rock concert 1 50 dB 3 90 dB 2 100 dB 4 60 dB

4 1454 Hz If we study the vibration of a pipe open at both ends then the following statement is not true NEET 2013 1 Odd harmonics of the fundamental frequency will be generated 2 All harmonics of he fundamental frequency will be generated 3 Pressure change will h

Problem 10 A bus is moving with a velocity of 5 m s towards a huge wall The driver sounds a horn of frequency 165 Hz If the speed of sound in air is 335 m s the number of beats heard per second by the passengers in the bus will be 1 3 3 5 2 4 4 6

2 y sin 10 x 20nt 3 y sin 2x 2 t 4 y sin x 2t Dis aus 20 Two sources of sound placed close to each other are emitting progressive waves given by Y 4 sin600 t and y 5 sin 608 t An observer located near these two sources of sound will hear AIPMT Prelims 2012 1 8 beats per second with intensity ratio 81 1 between waxing and waning 2 4 beats per second with intensity ratio 81 1 between waxing and waning 3 4 beats per second with intensity ratio 25 16 between waxing and waning 4 8 beats per second with intensity ratio 25 16 between waxing and waning When a string is divided into three segments of length 1 12 and 13 the fundamental frequencies of these thron

Problem 3 Plane simple harmonic progressive waves of wavelengths 120 cm and speed 34800 cm sec are incident normally on a plane surface which is a perfect reflector of sound Stationary waves are formed The ratio of amplitudes of vibrations at points distant i 10 cm ii 30 cm from the reflector is 1 3 1 2 1 1 2 1 0 4 1 4

Problem 13 A vehicle with a horn of frequency n is moving with a velocity of 30 m s in a direction perpendicular to the straight line joining the observer and the vehicle The observer perceives the sound to have a frequency n n Then n is equal to take velocity of sound in air as 330 m s n n n 0 1 M 3 n 0 1n 10n 2 4

Problem 8 A source of sound of frequency 256 Hz is moving towards a wall with a velocity of 5 m s The velocity of sound is 330 m s The numbher of beats heard by an observed moving along with the sounding object is 1 256x 3 330 325 256 256 330 225 256 330 325 2 256 4 256 330 335 335 325 256x 256

Problem 2 In a gas two waves of wavelengths 1m and 1 01 m are superposed and produce 10 beats in 3 seconds The velocity of sound in the medium is 1 300 m s 3 360 2 m s 2 336 7 m s 4 270 m s

Two sources of sound are separated by a distance 4 m They both emit sound with the same amplitude and frequency 330 Hz but they are 180 out of phase At what points between the two sources will the sound intensity be maximum Ans 0 25 0 75 1 25 and 1 75 m from the point at the center

S S are two coherent sources of sound along x axis separated by 42 where is wavelength of sound emitted by them Number of maximum located on the elliptical boundary around it will be 101 S anot muk 42 1 16 2 12 S 3 8 4 4

NEET AIIMS 18 A policeman on duty detects a drop of 10 in the pitch of the horn of motion of car as it crosses him If the velocity of sound is 330 m s Calculate the speed of the car 1 17 4 m s 2 20 4 m s 3 18 6 m s 4 16 4 m s ift fo pounds a whistle of frequency 640 Hz when 1 km heard by

34 Find the acceleration of the blocks A and B in the three situations shown in figure 5 E17 B 35 kg a 4 kg A 2 kg B b 5 kg 1 kg B 1A c 2 kg

The maximum no of possible interference maxima for slit seperation equal to twice the wavelength in Young s double slit expt is a infinite b five c three d zero

moisture in hydrogen gas increases at a given temperature 1 Increase the speed of sound in the gas will OL asiged 2 Decrease 3 Remain the same B Any of the above depending on the temperature of the gas

A source of sound emitting a note of frequency 200 Hz moves towards an observer with a velocity v equal to the velocity of sound If the observer also moves away from the source with the same velocity v the apparent frequency heard by the observer is a 189 Hz b 218 6 Hz c 200 Hz d zero

Example 17 45 i An engine approaches a hill with a constant speed When it is at a distance of 0 8 km it blows a whistle whose echo is heard by the driver after 4 s If speed of engine in air is 330 m s Calculate the speed of engine ii A person standing between two parallel hills fires a gun He hears the first echo after 1 5 s and second after 2 5 s If speed of sound is 332 m s calculate he distance between the hills When will he hear the third echo

Which of the following statements is incorrect 1 In solids longitudinal waves travel faster than transverse waves 2 Reverberation time in an auditorium increases if the volume of enclosure increases 3 Phenomenon of beats can be observed between sound sources of different nature 4 Doppler s effect in sound is symmetrical

In resonance tube first resonanting length is 25 cm then its second resonanting length will be if e 0

9 Each of the two strings of length 51 6 cm and 49 1 cm are tensioned separately by 20 N force Mass per unit length of both the strings is same and equal to 1 g m When both strings vibrate simultaneously the number of beats is AIPMT Prelims 2009 1 7 3 3 2 8 4 5

C bauce lo Hand A standing wave is created on a string of length 120 m and it is vibrating in 6th harmonic Maximum amplitude of any particle is 10 cm and maximum possible velocity will be 10 cm s Choose the corre Illustration 26 ment 1 Angular wave number of two waves will be ar 2 Time period of any particle s SHM will be 4n sec 3 Any particle will have same kinetic energy as potential energy lain sh ont moi berlai 4 Amplitude of interfering waves are 10 cm each olution 6 2 120 40 k TC 20 Aw Vn TC 20 max 1 T 2T ab A

18 A policeman on duty detects a drop of 10 in the pitch of the horn of motion of car as it crosses him velocity of sound is 330 m s Calculate the speed of the car 1 17 4 m s v 2 20 4 m s 3 18 6 m s 4 16 4 m s Whistle of frequency 640 Hz wher ency is

A source of sound is moving towards a high wa with a speed 20 m s The frequency of the soun produced by the source is 400 Hz If the soun travels at 30 m s what will be beat frequency hear by a man standing near the wall

RACE 03 a stationary wave the amplitude corresponding to antinode is 4 cm then the amplitude corresponding to a particle of medium located exactly midway between a node and an antinode is 1 2 cm 2 2 2 cm 3 2 cm 4 1 5 cm

28 96 A sound source is moving with speed 5 m s towards a wall If the velocity of sound is 330 m s the tationary observer would hear beats is equal to frequency of source 240 Hz H

X 2 There are three sources of sound of equal intensity with frequency 200 Hz 201 Hz and 202 Hz respectively if all sounded simultaneously then beat frequency heard by listener is 1 2 2 3 3 1

A train whistling at constant frequency is moving towards a station at a constant speed The train goes past a stationary observer on the station The variation of frequency fof the sound as heard by the observer as a function of time t is best represented by 1 3 2 4 t