# Engineering Physics Questions and Answers – Progressive Waves

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

1. The ratio of velocity of sound in hydrogen and oxygen at STP is __________
a) 16:1
b) 8:1
c) 4:1
d) 2:1

Explanation: vH/vO = √(MO/MH)
=√(32/2)=4:1.

2. It takes 2 seconds for a sound wave to travel between two fixed points when the day temperature is 10°C. If the temperature rises to 30°C, the sound wave travels between the same fixed parts in __________
a) 1.9s
b) 2s
c) 2.1s
d) 2.2s

Explanation: v∝√T
t∝1/v
t∝1/√T
t2/t1 = √(T1/T2)=√((273+10)/(273+30))=√(283/303)
t2=√(283/303)×2s=1.9s.

3. The disc of a siren containing 60holes rotates at a constant speed of 360rpm. The emitted sound is in unison with a tuning fork of frequency.
a) 10Hz
b) 360Hz
c) 216Hz
d) 60Hz

Explanation: Frequency of revolution of disc=360rpm=360/60rps=60rps
Frequency of emitted sound=6×No.of holes
=6×60=360Hz.

4. The quantity which does not change, when sound enters from one medium to another __________
a) Wavelength
b) Speed
c) Frequency
d) Velocity

Explanation: Frequency remains unchanged when sound travels from one medium to another.

5. The equation of a simple harmonic wave is given by
y=5sin⁡(π/2) (100t-x)
Where x and y are in metre and time is in second. The period of the wave in second will be __________
a) 0.04
b) 0.01
c) 1
d) 5

Explanation: y=5sin⁡(π/2) (100t-x)
y=Asin(ωt-kx)
ω=2π/T=π/2×100
T=2/50=0.04s.
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6. If wave y=Acos(ωt+kx) Is moving along x-axis, the shapes of a pulse at t=0 and t=2s.
a) Are different
b) Are same
c) May not be the same
d) Unpredictable

Explanation: The shapes of y-x graph remains the same at t=0 and t=2s.

7. y1=4sin⁡(ωt+kx), y2=-4cos⁡(ωt+kx), the phase difference is __________
a) π/2
b) 3π/2
c) π
d) Zero

Explanation: y1=4sin⁡(ωt+kx)
y2=-4cos⁡(ωt+kx)
=-4sin⁡(ωt+kx+3π/2)
∆φ=3π/2.

8. A wave equation is y=0.1sin[100πt-kx] and wave velocity is 100m/s, its number is equal to __________
a) 1/m
b) 2/m
c) π/m
d) 2π/m

Explanation: y=0.1sin⁡[100πt-kx]
y=Asin(ωt-kx)
ω=100π
Wave number=ω/v=100π/100=π/m.

9. A particle on the trough of a wave at any instant will come to the mean position after a time (T=time period).
a) T/2
b) T/4
c) T
d) 2T

Explanation: Time taken by a particle to move from trough to the mean position=T/4.

10. A string is tied on a sonometer, second end is hanging downward through a pulley with tension T. The velocity of the transverse wave produced is proportional to __________
a) 1/√T
b) √T
c) T
d) 1/T

Explanation: v=√(T/m)
v∝√T.

11. The fundamental frequency of a sonometer wire is n. If the tension is made 3 times and length and diameter are also increased 3 times, the new frequency will be __________
a) 3n
b) n/3√3
c) n/3
d) √3 n

Explanation: n=1/LD×√(T/πρ)
n=1/(3L×3D)×√(3T/πρ)=√3/9×n=1/(3√3) n.

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