JEE Questions for Physics Waves Quiz 18 - MCQExams.com

A source is moving towards an observer with a speed of 20 m/s and having frequency of 240 Hz. The observer is now moving towards the source with a speed of 20 m/s. Apparent frequency heard by observer, if velocity of sound is 340 m/s, is
  • 240 Hz
  • 270 Hz
  • 280 Hz
  • 360 Hz
A whistle revolves in a circle with an angular speed of 20 rad/sec using a string of length 50 cm. If the frequency of sound from the whistle is 385 Hz, then what is the minimum frequency heard by an observer, which is far away from the centre in the same plane ? (v = 340 m/s)
  • 333 Hz
  • 374 Hz
  • 385 Hz
  • 394 Hz
A siren emitting sound of frequency 800 Hz is going away from a static listener with a speed of 30 m/s, frequency of the sound to be heard by the listener is (take velocity of sound as 330 m/s)
  • 733.3 Hz
  • 644.8 Hz
  • 481.2 Hz
  • 286.5 Hz
What should be the velocity of a sound source moving towards a stationary observer so that apparent frequency is double the actual frequency (Velocity of sound is v)

  • Physics-Waves-97123.png
  • 2)
    Physics-Waves-97124.png

  • Physics-Waves-97125.png

  • Physics-Waves-97126.png
A source and an observer approach each other with same velocity 50 m/s. If the apparent frequency is 435 sec–1, then the real frequency is
  • 320 sec–1
  • 360 sec–1
  • 390 sec–1
  • 420 sec–1
Doppler effect is applicable for
  • Moving bodies
  • One is moving and other are stationary
  • For relative motion
  • None of the above
When an engine passes near to a stationary observer then its apparent frequencies occurs in the ratio 5/3. If the velocity of engine is (Velocity of sound is 340 m/s)
  • 540 m/s
  • 270 m/s
  • 85 m/s
  • 52.5 m/s
A bat flies at a steady speed of 4 ms–1 emitting a sound of f = 90 x 103 Hz. It is flying horizontally towards a vertical wall. The frequency of the reflected sound as detected by the bat will be (Take velocity of sound in air as 330 –1).
  • 88.1 x 103 Hz
  • 87.1 x 10–3 Hz
  • 92.1 x 103 Hz
  • 89.1 x 103 Hz
A source is moving towards a stationary observer, so that the apparent frequency increases by 50%. If velocity of sound is 330 ms-1, then velocity of source is
  • 220 ms–1
  • 180 ms–1
  • 150 ms–1
  • 110 ms–1
Which of the following has high pitch in their sound?
  • Lion
  • Mosquito
  • Man
  • Woman
A spherical source of power 4 W and frequency 800 Hz is emitting sound waves. The intensity of waves at a distance 200 m is
  • 8 x 10–6W/m 2
  • 2 x 10–4 W/m 2
  • 1 x 10–4 W/m 2
  • 4 W/m 2
If the pressure amplitude in a sound wave is tripled, then the intensity of sound is increased by a factor of
  • 9
  • 3
  • 6
  • √3

Physics-Waves-97138.png
  • 3000
  • 1000
  • 300
  • 30
Decibel is unit of
  • Intensity of light
  • X-rays radiation capacity
  • Sound loudness
  • Energy of radiation
When we hear a sound, we can identify its source from
  • Amplitude of sound
  • Intensity of sound
  • Wavelength of sound
  • Overtones present in the sound
A man x can hear only upto 10 kHz and another many upto 20 kHz. A note of frequency 500 Hz is produced before them from a stretched string. Then
  • Both will hear sounds of same pitch but different quality
  • Both will hear sounds of different pitch but same quality
  • Both will hear sounds of different pitch and different quality
  • Both will hear sounds of same pitch and same quality
A is singing a note and at the same time B is singing a note with exactly one-eighth the frequency of the note of A. The energies of two sounds are equal, the amplitude of the note of B is
  • Same that of A
  • Twice as that of A
  • Four times as that of A
  • Eight times as that of A
The intensity of sound from a radio at a distance of 2 metre from its speaker is 1 x 10–2 µ W/m2. The intensity at a distance of 10 meters would be
  • 0.2 x 10-2 µ W/m2
  • 1 x 10-2 µ W/m2
  • 4 x 10-4 µ W/m2
  • 5 x 10-2 µ W/m2
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 of room A?

  • Physics-Waves-97149.png
  • 1
  • 2
  • 4
A sound absorber attenuates the sound level by 20 dB.The intensity decreases by a factor of
  • 1000
  • 10000
  • 10
  • 100
If separation between screen and source is increased by 2% what would be the effect on the intensity ?
  • Increases by 4%
  • Increases by 2%
  • Decreases by 2%
  • Decreases by 4%
Quality depends on
  • Intensity
  • Loudness
  • Timbre
  • Frequency
Intensity level 200 cm from a source of sound is 80 dB. If there is no loss of acoustic power in air and intensity of threshold hearing is 10–2 Wm–2 then, what is the intensity level at a distance of 4000 cm from source?
  • Zero
  • 54 dB
  • 64 dB
  • 44 dB
A point source emits sound equally in all directions in a non-absorbing medium. Two points P and Q are at distances of 2m and 3m respectively from the source. The ratio of the intensities of the waves at P and Q is
  • 9 : 4
  • 2 : 3
  • 3 : 2
  • 4 : 9
Each of the properties of sound listed in column A primarily depends on one of the quantities in column B. Choose the matching pairs from two columns
Physics-Waves-97158.png
  • Pitch-Waveform, Quality-Frequency; Loudness¬Intensity
  • Pitch-Frequency, Quality-Waveform; Loudness-Intensity
  • Pitch-Intensity, Quality-Waveform; Loudness-Frequency
  • Pitch-Waveform, Quality- Intensity; Loudness-Frequency
A train has just completed a U-curve in a track which is a semicircle. The engine is at the forward end of the semicircular part of the track while the last carriage is at the rear end of the semicircular track. The driver blows a whistle of frequency 200 Hz. Velocity of sound is 340 m/sec. Then the apparent frequency as observed by a passenger in the middle of a train when the speed of the train is 30 m/sec is
Physics-Waves-97160.png
  • 209 Hz
  • 288 Hz
  • 200 Hz
  • 181 Hz
Two cars are moving on two perpendicular roads towards a crossing with uniform speeds of 72 km/hr and 36 km/hr. If first car blows horn of frequency 280 Hz, then the frequency of horn heard by the driver of second car when line joining the cars make 45° angle with the roads; will be
  • 321 Hz
  • 298 Hz
  • 289 Hz
  • 280 Hz
An observer moves towards a stationary source of sound with a speed 1/5th of the speed of sound. The wavelength and frequency of the source emitted are X and f respectively. The apparent frequency and wavelength recorded by the observer are respectively
  • 1.2f, λ
  • f, 1.2 λ
  • 0.8 f, 0.8 λ
  • 1.2 f, 1.2 λ

Physics-Waves-97176.png
  • 1 : 2
  • 2 : 1
  • 1 : 1
  • None of these

Physics-Waves-97178.png

  • Physics-Waves-97179.png
  • 2)
    Physics-Waves-97180.png

  • Physics-Waves-97181.png

  • Physics-Waves-97182.png
Consider ten identical sources of sound all giving the same frequency but having phase angles which are random. If the average intensity of each source is Io, the average of resultant intensity I due to all these ten sources will be

  • Physics-Waves-97184.png
  • 2)
    Physics-Waves-97185.png

  • Physics-Waves-97186.png

  • Physics-Waves-97187.png
16 tunning forks are arranged in the order of increasing frequencies. Any two successive forks give 8 beats per sec when sounded together. If the frequency of the last fork is twice the first, then the frequency of the first fork is
  • 120
  • 160
  • 180
  • 220
Two identical straight wires are stretched so as to produce 6 beats per second when vibrating simultaneously. On changing the tension in one of them, the beat frequency remains unchanged. Denoting by T1, T2, the higher and the lower initial tensions in the strings, then it could be said that while making the above change in tension
  • T2 was decreased
  • T2 was increased
  • T1 was increased
  • T1 was kept constant
A man is watching two trains, one leaving and the other coming in with equal speeds of 4 m/sec. If they sound their whistles, each of frequency 240 Hz, the number of beats heard by the man (velocity of sound in air = 320 m/sec) will be equal to
  • 6
  • 3
  • 0
  • 12
Two speakers connected to the same source of fixed frequency are placed 2.0 m apart in a box. A sensitive microphone placed at a distance of 4.0m from their midpoint along the perpendicular bisector shows maximum response. The box is slowly rotated until the speakers are in line with the microphone. The distance between the midpoint of the speakers and the microphone remains unchanged. Exactly five maximum responses are observed in the microphone in doing this. The wavelength of the sound wave is
  • 0.2 m
  • 0.4 m
  • 0.6 m
  • 0.8 m
A wire of 9.8 x 10–3 kgm –1 passes over a frictionless light pulley fixed on the top of a frictionless inclined plane which makes an angle of 30° with the horizontal. Masses m and M are tied at the two ends of wire such that m rests on the plane and M hangs freely vertically downwards. The entire system is in equilibrium and a transverse wave propagates along the wire with a velocity of 100 ms–1. Choose the correct option
Physics-Waves-97197.png
  • m = 20 kg
  • m = 5 kg
  • m = 2 kg
  • m = 7 kg
Two loudspeakers L1 and L 2 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 the speed of sound is 330 ms–1 then the frequency at which the first maximum is observed is
Physics-Waves-97200.png
  • 165 Hz
  • 330 Hz
  • 496 Hz
  • 660 Hz
A person speaking normally produces a sound intensity of 40 dB at a distance of 1 m. If the threshold intensity for reasonable audibility is 20 dB, the maximum distance at which he can be heard clearly is
  • 4 m
  • 5 m
  • 10 m
  • 20 m
Vibrating tuning fork of frequency n is placed near the open end of a long cylindrical tube. The tube has a side opening and is fitted with a movable reflecting piston. As the piston is moved through 8.75 cm, the intensity of sound changes from a maximum to minimum. If the speed of sound is 350 m/s. Then n is
Physics-Waves-97203.png
  • 500 Hz
  • 1000 Hz
  • 2000 Hz
  • 4000 Hz

Physics-Waves-97210.png
  • Moving along y direction with frequency 2n x 106 Hz and wavelength 200 m
  • Moving along x direction with frequency 106 Hz and wavelength 100 m
  • Moving along x direction with frequency 106 Hz and wavelength 200 m
  • Moving along –x direction with frequency 106 Hz and wavelength 200 m
Three waves of equal frequency having amplitudes 10 gm, 4µm and 7 gm arrive at a given point with successive phase difference of π /2. The amplitude of the resulting wave in gm is given by
  • 7
  • 6
  • 5
  • 4
An organ pipe is closed at one end has fundamental frequency of 1500 Hz . The maximum number of overtones generated by this pipe which a normal person can hear is
  • 14
  • 13
  • 6
  • 9
An earthquake generates both transverse (S) and longitudinal (P) sound waves in the earth. The speed of S waves is about 4.5 km/s and that of P waves is about 8.0 km/s. A seismograph records P and S waves from an earthquake. The first P wave arrives 4.0 min before the first S wave. The epicenter of the earthquake is located at a distance about
  • 25 km
  • 250 km
  • 2500 km
  • 5000 km
A student is performing the experiment of resonance column. The diameter of the column tube is 4cm. The frequency of the tuning fork is 512Hz. The air temperature is 38°C in which the speed of sound is 336 m/s. The zero of the meter scale coincides with the top end of the resonance column tube. When the first resonance occurs, the reading of the water level in the column is
  • 14.0 cm
  • 15.2 cm
  • 16.4 cm
  • 17.6 cm
When a string is divided into three segments of length l1,l2 and l 3 the fundamental frequencies of these three segments are v1, v2 and v3 respectively. The original fundamental frequency (v) of the string is

  • Physics-Waves-97222.png
  • 2)
    Physics-Waves-97223.png

  • Physics-Waves-97224.png

  • Physics-Waves-97225.png
The rope shown at an instant is carrying a wave travelling towards right, created by a source vibrating at a frequency n. Consider the following statements
Physics-Waves-97227.png
  • I, II and III
  • II only
  • I and III
  • III only
A man is standing on a railway platform listening to the whistle of an engine that passes the man at constant speed without stopping. If the engine passes the man at time to. How does the frequency f of the whistle as heard by the man changes with time?

  • Physics-Waves-97228.png
  • 2)
    Physics-Waves-97229.png

  • Physics-Waves-97230.png

  • Physics-Waves-97231.png
The figure shows four progressive waves A, B, C, and D with their phases expressed with respect to the wave A. It can be concluded from the figure that
Physics-Waves-97232.png
  • The wave C is ahead by a phase angle of π / 2 and the wave B lags behind by a phase angle of π /2
  • The wave C lags behind by a phase angle of it π /2 and the wave B is ahead by a phase angle of π /2
  • The wave C is ahead by a phase angle of π and the wave B lags behind by a phase angle of π
  • The wave C lags behind by a phase angle of π and the wave B ahead by a phase angle of π
The diagram below shows the propagation of a wave. Which points are in same phase?
Physics-Waves-97233.png
  • F, G
  • C and E
  • B and G
  • B and F
The diagram below shows an instantaneous position of a string as a transverse progressive wave travels along it from left to right
Which one of the following correctly shows the direction of the velocity of the points 1, 2 and 3 on the string?
Physics-Waves-97234.png
  • 1 = →, 2 = →, 3 = →
  • 1= →, 2 = ←, 3 = →
  • 1 = ↓, 2 = ↓, 3 = ↓
  • 1 = ↓, 2 = ↑, 3 = ↓
0:0:1


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