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A car moves at a speed of 20 ms^-1sounding its horn at 480 Hz. If the speed of sound is 340 ms ^-1, the frequency of the reflected sound heard by the girl sitting in the car will be closest to

a) 540 hz b) 524 Hz c) 568 Hz d) 480 Hz Answer: a) 540 hz Solution: f'' = 540 Hz... View Article

A string of length 2 m is fixed at both ends. If this string vibrates in its fourth normal mode with a frequency of 500 Hz, then the waves would travel on it with a velocity of

a) 125 ms-1 b) 250 ms-1 c) 500 ms-1 d) 1000 ms-1 Answer: c) 500 ms-1 Solution: For string λ=2l/p where p= number of... View Article

If in a resonance tube, oil of density higher than that water is used, then at the resonance, frequency would

a) increase b) decrease c) slightly increase d) remains same Answer: d) remains same Solution: The frequency is independent of... View Article

On which principle does the sonometer work?

a) Hooke's law b) Elasticity c) Resonance d) Newton's law Answer: c) Resonance Solution: Sonometer works on the principle of... View Article

In the fundamental mode, the time taken by the wave to reach the closed end of the air-filled pipe is 0.01 s. The fundamental frequency is

a) 25 b) 12.5 c) 20 d) 15 Answer: a) 25 Solution: Time taken to reach the closed end=l/v =0.01s Frequency, f = v/λ =... View Article

In a resonance tube, using a tuning fork of frequency 325 Hz, two successive resonance lengths are observed as 25.4 cm and 77.4 cm respectively. The velocity of sound in air is

1) 338 ms-1 2) 328 ms-1 3) 330 ms-1 4) 320 ms-1 Answer: 1) 338 ms-1 Solution: V = 2f (l2 - l1) = 2 x 325(77.4 - 25.4) x... View Article

Find beat frequency. Motion of two particles is given by y₁ = 0.25 sin (310t) and y₂ = 0.25 sin (316t)

a) 3 b) 3/π c) 6/π d) 6 Answer: b) 3/π Solution: y = A sin ωt Given, y1 = 0.25 sin (310t) y2 = 0.25 sin... View Article

A hollow pipe of length 0.8 m is closed at one end. At its open end, a 0.5 m long uniform string is vibrating in its second harmonic and it resonates with the fundamental frequency of the pipe. If the tension in the wire is 50 N and the speed of sound is 320 ms ^-1, the mass of the string is

a) 5 g b) 10 g c) 20 g d) 40 g Answer: b) 10 g Solution: The fundamental frequency of pipe = frequency of second harmonic of... View Article

Choose the correct statement.

a) Beats are due to destructive interference b) Maximum beat frequency audible to a human being is 20 c) Beats are a result of Doppler's... View Article

Two waves of wavelength 1.00 m and 1.01 m produces 10 beats in 3 s. What is the velocity of the wave?

a) 150 ms-1 b) 115.2 ms-1 c) 336.6 ms-1 d) 200 ms-1 Answer: c) 336.6 ms-1 Solution: λ1 = 1 m λ2= 1.01 m Number... View Article

Three sound waves of equal amplitudes have frequencies (v –1), v, (v + 1). They superimpose to give the beat. The number of beats produced per second will be

a) 4 b) 3 c) 2 d) 1 Answer: c) 2 Solution: f1 = v - 1 f2 = v f3 = v + 1 Maximum number of beats will be, n = f3 - f1 n =... View Article

How many times more intense is a 60 dB sound than a dB sound?

a) 1000 b) 2 c) 100 d) 4 Answer: a) 1000 Solution: L = 10 log10(I/I0) 60 = 10 log10(I1/I0) (I1/I0) = 106 ------(1) Similarly, 30 = 10... View Article

The disc of a siren containing 60 holes rotates at a constant speed of 360 rpm. The emitted sound is in unison with a tuning fork of frequency

a) 10 Hz b) 360 Hz c) 216 Hz d) 60 Hz Answer: b) 360 Hz Solution: Number of holes in the disc = 60 The number of holes in the disc... View Article

Doppler phenomenon is related with

a) pitch (frequency) b) loudness c) quality d) reflection Answer: a) pitch (frequency) Solution: Doppler Effect: When the source... View Article

Two trains, each moving with a velocity of 30 ms ^-1, cross each other. One of the trains gives a whistle whose frequency is 600 Hz. If the speed of sound is 330 ms^-1, the apparent frequency for passengers sitting in the other train before crossing would be

a) 600 Hz b) 630 Hz c) 920 Hz d) 720 Hz Answer: d) 720 Hz Solution: As source and observer are moving towards each other with... View Article

A car sounding its horn at 480 Hz moves towards a high wall at a speed of 20 ms^-1. If the speed of sound is 340 ms ^-1, the frequency of the reflected sound heard by the girl sitting in the car will be closest to

a) 540 Hz b) 524 Hz c) 568 Hz d) 480 Hz Answer: a) 540 Hz Solution: After reflection from the wall, the sound moves towards the... View Article

The change in frequency due to Doppler’s effect does not depend on

a) the speed of the source b) the speed of the observer c) the frequency of the source d) separation between the source and the observer... View Article

A train is approaching with velocity 25 ms ^-1 towards a pedestrian standing on the track, frequency of horn of train is 1 kHz. The frequency heard by the pedestrian is (take, v = 350 ms ^-1 )

a) 1077 Hz b) 1167 Hz c) 985 Hz d) 954 Hz Answer: a) 1077 Hz Solution: Given, v = 350 m/s v = 1 Khz = 1000 vs = 25... View Article

A car is moving with a speed of 72 km–h ^-1 towards a roadside source that emits found at a frequency of 850 Hz. The car driver listens to the sound while approaching the source and again while moving away from the source after crossing it. If the velocity of sound is 340 ms ^-1, the difference between the two frequencies, the driver hears is

a) 50 Hz b) 85 Hz c) 100 Hz d) 150 Hz Answer: c) 100 Hz Solution: By Doppler's Effect When the observer is moving with... View Article

In 1 m long open pipe, what is the harmonic of resonance obtained with a tuning fork of frequency 480 Hz?

a) First b) Second c) Third d) Fourth Answer: c) Third Solution: Frequency of Nth harmonic, n = NV/2l v = speed of sound l =... View Article