Engineering Physics Question Bank focuses on “Sounds and Waves – 2”.
1. At what temperature, the speed of sound in the air will become double of its value at 27°C?
a) 54°C
b) 627°C
c) 327°C
d) 927°C
Answer: d
Clarification: As of v∝√T
v/2v=√((273+27)/T)
T=1200K=927℃.
2. The speed of a wave in a medium is 760m/s. If 3600 waves are passing through a point in the medium in 2 min, then its wavelength is?
a) 13.8m
b) 41.5m
c) 25.3m
d) 57.2m
Answer: c
Clarification: Number of waves crossing a point per second,
γ=3600/(2×60)=30
ʎ=v/γ=760/30=25.3m.
3. An underwater sonar source operating at a frequency of 60 kHz directs its beam towards the surface. If velocity of sound in air is 330m/s, wavelength and frequency of the waves in air are ___________
a) 5.5mm, 60 kHz
b) 5.5mm, 30 kHz
c) 5.5mm, 30 kHz
d) 5.5mm, 80 kHz
Answer: a
Clarification: Frequency in air will also be 60 kHz
ʎa=va/γ=330/(60×103)=5.5×10-3 m
=5.5mm.
4. A wave of frequency 100Hz travels along a string towards its fixed end. When this wave travels back, after reflection, a node is formed at a distance of 10cm from the fixed end. The speed of the wave (incident and reflected) is?
a) 5m/s
b) 20m/s
c) 10m/s
d) 40m/s
Answer: b
Clarification: Distance between two successive nodes=ʎ/2=10cm
ʎ=20cm
v=γʎ=100×20=2000=20m/s.
5. The first overtone of a stretched wire of given length is 320Hz. The first harmonic is ___________
a) 320Hz
b) 160Hz
c) 480Hz
d) 640Hz
Answer: b
Clarification: First overtone=2γ=320Hz
First harmonics=γ=160Hz.
6. For beats to be produced ___________
a) Frequency of sources should be different and amplitude should be the same
b) Frequency of sources should be same and amplitude should be different
c) Frequency of sources should be same and amplitude should be different
d) Frequency of sources should be same and amplitude should be the same
Answer: a
Clarification: For beats formation, frequency of sources should be slightly different and amplitude should be the same.
7. Sources of sound and observer are moving towards each other, the observer will hear ___________
a) High frequency, low wavelength
b) Low frequency, low wavelength
c) High frequency, low wavelength
d) Low frequency, high wavelength
Answer: c
Clarification: When source and observer approach each other, frequency of sound increases while wavelength decreases.
8. Reverberation time can’t be controlled by ___________
a) Temperature
b) Size of window
c) Volume of room
d) Changing carpet
Answer: d
Clarification: Reverberation time is the time which sound takes to fall in intensity to one millionth part of its original intensity.
9. Pressure variation of a mechanical wave depends upon ___________
a) ∝Intensity
b) Independent of intensity
c) ∝1/Intensity
d) Intensity2
Answer: c
Clarification: Pressure amplitude vibration in a medium∝Amplitude of the wave (A)
Hence pressure variation is proportional to the intensity of the wave.
10. 50 tuning forks are arranged in increasing order of their frequencies such that each gives 4 beats/sec with its previous tuning fork. If the frequency of the last fork is an octave of the first, then the frequency of the first tuning fork is?
a) 200Hz
b) 204Hz
c) 196Hz
d) 0