Engineering Physics Questions and Answers – Travelling Waves

This set of Engineering Physics Multiple Choice Questions & Answers (MCQs) focuses on “Travelling Waves”.

1. When the length of the vibrating segment of a sonometer wire is increased by 1%, the percentage change in its frequency is?
a) 100/101
b) 99/100
c) 1
d) 2

Explanation: v=1/2L×√(T/m)
For constant T and m,
∆v/v×100=∆L/L×100=1%
Frequency will decrease by 1%.

2. In an experiment with sonometer a tuning fork of frequency 256Hz resonates with a length of 25cm and another tuning fork resonates with a length of 16x\cm. Tension of the spring remaining constant the frequency of the second tuning fork is?
a) 163.84Hz
b) 400Hz
c) 320Hz
d) 20.4Hz

Explanation: v∝1/L
v2/v1 = L1/L2
v2=L1/L2 ×v1=25/16×256=400Hz.

3. An open pipe resonates with a tuning fork of frequency 500Hz. It is observed that two successive nodes are formed at distances 16 and 46cm from the open end. The speed of sound in air in the pipe is?
a) 230 m/s
b) 300 m/s
c) 320 m/s
d) 360 m/s

Explanation: v=2γ(l2-l1)
v=2×500(46-16)cm/s
=30000cm/s=300m/s.

4. The velocity of sound in open ended tube in 330m/s, the frequency of a wave is 1.1 kHz and length of the tube is 30cm, then number of harmonics that it will emit is?
a) 2
b) 3
c) 4
d) 5

Explanation: For an open tube,
vn=nv/2L
1.1×103=(n×330)/(2×0.30)
n=2.

5. An organ pipe, open at both ends produce 5 beats per second when vibrated with a source of frequency 200Hz. The second harmonic of the same pipe produces 10 beats per second with a source of frequency 420 Hz. The frequency of source is?
a) 195Hz
b) 205Hz
c) 190Hz
d) 210Hz

Explanation: Fundamental frequency of open pipe,
f=200±5=195Hz or 205Hz
Second harmonics of open pipe,
2f=420±10=410Hz or 430Hz
f=205Hz or 215Hz.

6. Following two wave trains are approaching each other
y1=asin200πt, y2=asin208πt.
The number of beats heard per second is?
a) 8
b) 4
c) 1
d) Zero

Explanation: ω1=2πv1=200π or v1=100Hz
ω2=2πv2=208π or v2=105Hz
Beat frequency=v2-v1=4Hz.

7. Two waves of wavelength 99cm and 100cm both travelling with velocity 396m/s are made to interfere. The number of beats produced by them per second is?
a) 1
b) 2
c) 4
d) 8

Explanation: Beat frequency=v[(1/ʎ1)-(1/ʎ2)] =396[(1/0.99)-(1/1)]=4Hz.

8. Two waves are propagating with the same amplitude and nearly same frequency in opposite direction, they result in __________
a) Beats
b) Stationary wave
c) Resonance
d) Wave packet

Explanation: Stationary waves are formed when two waves of same frequency travelling in opposite directions are superimposed.

9. A tuning fork A produces 4beats/s with another tuning fork B of frequency 320Hz. On filing one of the prongs of A, 4beats/s is again heard when sounded with the same fork B. Then, the frequency of the fork A before filing is __________
a) 328Hz
b) 316Hz
c) 324Hz
d) 320Hz

Explanation: Frequency of A=320±4=324 or 316Hz. As frequency increases on filing, so frequency of A=316Hz (lower value).

10. A source emits a sound of a frequency of 400Hz, but the listener hears it’s to be 390Hz. Then?
a) The listener is moving towards the source
b) The source is moving towards the listener
c) The listener is moving away from the source
d) The listener has a defective ear

Explanation: As apparent frequency is lesser than the actual frequency, the listener is moving away from the source.

Sanfoundry Global Education & Learning Series – Engineering Physics.

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