A cylindrical tube open at both ends has a fundamental frequency f in air. The tube is dipped vertically in water so that half of it is in water. The fundamental frequency of the air column is now a) f/2 b) f c) 3f/4 d) 2f Answer: b) f Solution: Case 1: λ/2 = l ⇒ λ = 2l f = v/λ = v/2l Case... View Article
Two waves are represented by, y1 = A sin (kx – ωt) and y2 = A cos (kx – ωt) The amplitude of the resultant wave is 1) 4A 2) 2A 3) √2 A 4) A Answer: 3) √2 A Solution: y1 = A sin... View Article
Two points on a travelling wave having frequency 500 Hz and velocity 300 ms-1 are 600 out of phase, then the minimum distance between the two points is a) 0.2 b) 0.1 c) 0.5 d) 0.4 Answer: b) 0.1 Solution: As, v=nλ Therefore, λ=v/n=300/500=3/5m phase difference... View Article
The equation of a progressive wave can be given by y =15sin (660πt – 0.02πx). The frequency of the wave is a) 330 Hz b) 342 Hz c) 365 Hz d) 660 Hz Answer: a) 330 Hz Solution: y=15sin(660πt−0.02πx) The general... View Article
A pipe of length 85 cm is closed from one end. Find the number of possible natural oscillations of air column in the pipe whose frequencies lie below 1250 Hz. The velocity of sound in air is 340 m/s a) 12 b) 8 c) 6 d) 4 Answer: c) 6 In fundamental mode λ/4=0.85 λ=4×0.85 f =... View Article
Some of the frequencies of tones produced by an organ pipe are 220, 440, 550, 660 Hz. Find the effective length of the pipe. (take, the speed of sound in air = 330 m/s) a) 1.8 m b) 1.7 m c) 1.5 m d) 1.2 m Answer: c) 1.5 m Solution: Frequencies of tones produced by an organ pipe are 220,... 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: When both trains are moving towards each other then,... View Article
A car moves at a speed of 20 ms-1 sounding 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:Â a) 1000 Solution: L = 10 log10(I/I0) 60 =Â 10 log10(I1/I0) (I1/I0) = 106 ------(1) Similarly, 30 =Â 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
