A bus is moving with a velocity of 5 ms-1 towards a huge wall. The driver sounds a horn of frequency 165 Hz. If the speed of sound in air is 335 ms-1, the number of beats heard per second by a passenger inside the bus will be 1) 3 2) 4 3) 5 4) 6 5) 7 Answer: 3) 5 Solution: Apparent frequency, f'=f(v+vo)/(v−vs)... View Article
With what velocity should an observer approach stationary sound source, so that the apparent frequency of sound should appear double the actual frequency? (v is the velocity of sound) 1) v/2 2) 3v 3) 2v 4) v Answer: 4) v Solution: Given, f' = 2f f' = f[(v + v0)/(v + vs)] 2f = f[(v + v0)/(v)] 2v =... View Article
The speed of sound in air is 340 m/s. The speed with which a source of sound should move towards a stationary observer so that the apparent frequency becomes twice the original is 1) 640 ms-1 2) 340 ms-1 3) 170 ms-1 4) 85 ms-1 Answer: 3) 170 ms-1 Solution: Original frequency = f0 2f0 = f0[(v ±... View Article
The fundamental frequency of a segment of wire vibrating is 450 Hz and it is under a tension of 9 kg–wt. Then, tension at which the fundamental frequency of the same wire becomes 900 Hz is 1) 36 kg–wt 2) 27 kg–wt 3) 18 kg–wt 4) 72 kg–wt Answer: 1) 36 kg–wt Solution: n1 = k√T1 n2... View Article
A string fixed at both ends oscillates in 5 segments, length 10 m and the velocity of the wave is 20 ms-1. What is the frequency? 1) 5 Hz 2) 15 Hz 3) 10 Hz 4) 2 Hz Answer: 1) 5 Hz Solution: 5λ/2=L ⇒5λ/2=10 m Therefore,... View Article
When the length of the vibrating segment of a sonometer wire is increased by 1%, the percentage change in its frequency is 1) 100/101 2) 99/100 3) 1 4) 2 Answer: 3) 1 Solution: f = (1/2l)√(T/μ) Take log and differentiate, we get... View Article
An open organ pipe is closed suddenly with the result, that the second overtone of the closed pipe is found to be higher in frequency by 100 than the first overtone of the original pipe. Then, the fundamental frequency of the open pipe is 1) 200 s-1 2) 100 s-1 3) 300 s-1 4) 250 s-1 5) 150 s-1 Answer: 1) 200 s-1 Solution: Frequency of second overtone (fifth... View Article
A glass tube of length 1.0 m is completely filled with water. A vibrating tuning fork of frequency 500 Hz is kept over the mouth of the tube and the water is drained out slowly at the bottom of the tube. If the velocity of sound in air is 330 ms-1, then the total number of resonances, that occur will be 1) 2 2) 3 3) 1 4) 5 5) 4 Answer: 2) 3 Solution: λ = v/f = 330/500 = 0.66 m The resonance lengths are l1... View Article
The distance between nodes on a string is 5 cm. The velocity of the transverse wave is 2 ms -1. Then the frequency is 1) 5 Hz 2) 10 Hz 3) 20 Hz 4) 15 Hz Answer: 3) 20 Hz Solution: Distance between two nodes is λ/2 Therefore,... View Article
A closed organ pipe and an open organ pipe are tuned to the same fundamental frequency. The ratio of their lengths is 1) 1 : 1 2) 2 : 1 3) 1 : 4 4) 1 : 2 Answer: 4) 1 : 2 Solution: Avoiding end correction, the length of closed organ pipe, is... View Article
The frequency of the fundamental note in a wire stretched under tension T is f. If the tension is increased to 25 T. then the frequency of the fundamental note will be 1) 25f 2) 5f 3) 10f 4) f Answer: 2) 5f Solution: The fundamental frequency f=(1/2L)√(T/m) Therefore,... View Article
Two stretched strings have lengths l and 2l while tensions are T and 4T respectively. If they are made of same material, the ratio of their frequencies is 1) 2 : 1 2) 1 : 2 3) 1 : 1 4) 1 : 4 Answer:3) 1 : 1 Solution: Frequency is given by f=(1/2l)√(T/μ) Therefore, First... View Article
A sonometer wire 100 cm long has a fundamental frequency of 330 Hz. The velocity of propagation of transverse waves on the wire is 1) 330 ms-1 2) 660 ms-1 3) 990 ms-1 4) 115 ms-1 5) 550 ms-1 Answer: 2) 660 ms-1 Solution: For fundamental mode λ/2 =... View Article
In Young’s double-slit experiment, the distance between two sources is 0.1 mm. The distance of the screen from the sources is 20 cm. The wavelength of light used is 5460 Å Then the angular position of the first dark fringe is A. a) 0.08o b) 0.16o c) 0.20o d) 0.32o Answer: b) 0.16o Solution: Δx = dsinθ = λ/2 sinθ... View Article
When light is incident at a polarizing angle, which is completely polarised? a) reflected light b) refracted light c) both d) neither Answer: a) reflected light Solution: When the light is incident at the... View Article
Polaroid glass is used in sunglasses because a) it reduces the light intensity to half on account of polarization b) it is fashionable c) it has good colour d) it is cheaper... View Article
A light beam is incident at θ on an interface of air-glass such that the angle between reflected and the refracted beam is 900. Then θ is a) tan-1 (3/2) b) tan-12 c) tan-1 (3/4) d) tan-1 (4/3) Answer: a) tan-1 (3/2) Solution: When angle between reflected and... View Article
A plane wave of wavelength 6250 Å is incident normally on a slit of width 2 × 10-2 cm. The width of the principal maximum on a screen distant 50 cm will be a) 312.5 × 10-3 cm b) 31.25 × 10-3 cm c) 312 cm d) 312.5 × 10-3 mm Answer: a) 312.5 × 10-3 cm... View Article
The limit of resolution of eye is approximately a) 10 angle b) 1’ angle c) 1 mm d) 1 cm Answer: b) 1’ angle Solution: The resolution of the eye is the smallest... View Article
Diffraction pattern is obtained using red light. What will happen if it is replaced by violet light? a) Bands will disappear b) Bands will become narrow c) Bands will get spaced apart d) Bands will remain unchanged. Answer: b) Bands... View Article
