Engineering Physics Multiple Choice Questions on “Beats”.
1. If fundamental frequency is 50 and the next successive frequencies are 150 and 250, then it is __________
a) A pipe closed at both ends
b) A pipe closed at one end
c) An open pipe
d) A stretched string
Answer: b
Clarification: For a pipe closed at one end, higher frequencies are odd multiples of the fundamental frequency.
2. A stone thrown into still water creates a circular wave pattern moving radially outwards. If r is the distance measured from the centre to the pattern, the amplitude of the wave varies as __________
a) r(-1/2)
b) r(-1)
c) r(-3/2)
d) r(-2)
Answer: a
Clarification: For a circular wave,
I∝1/r
But A∝√I
A∝1/√r
A∝r(-1/2).
3. A siren emitting sound of frequency 800Hz is going away from a static listener with a speed of 30m/s. Frequency of the sound to be heard by the listener is (Take velocity of sound as 330m/s).
a) 733.3Hz
b) 644.8Hz
c) 481.2Hz
d) 286.5Hz
Answer: a
Clarification: γ‘=v/(v+vs)×γ=330/(330+30)×800
=733.3Hz.
4. An observer standing by the side of a road hears the siren of an ambulance, which is moving away from him. If the actual frequency of the siren is 2000Hz, then the frequency heard by the observer will be __________
a) 1990Hz
b) 2000Hz
c) 2100Hz
d) 4000Hz
Answer: a
Clarification: γ‘=1990
Apparent frequency decreases when the source moves away from the observer.
5. Statement: Sound wave cannot propagate fastest in solids.
Reason: Sound wave can propagate slightly in vacuum.
a) Both statement and reason are true and the reason is the correct explanation of the statement
b) Both statement and reason are true but the reason is not the correct explanation of the statement
c) Statement is true but the reason is false
d) Both statement and reason are false
Answer: c
Clarification: The statement is true but the reason is false. Sound waves, being mechanical waves, cannot propagate through a vacuum.
6. With the propagation of a longitudinal wave through a material medium, the quantities transmitted in the propagation direction are __________
a) Energy, momentum and mass
b) Energy
c) Energy and mass
d) Energy and linear momentum
Answer: b
Clarification: In wave propagation, energy is transmitted in the direction of propagation of the wave.
7. Which of the following statements is true?
a) Both light and sound waves can travel in the vacuum
b) Both light and sound waves in air are transverse
c) The sound waves in air are longitudinal while the light waves are transverse
d) Both light and sound waves in air are longitudinal
Answer: c
Clarification: The sound waves in air are longitudinal while the light waves are transverse.
8. The velocity of sound in any gas depends upon __________
a) Wavelength of sound only
b) Density and elasticity of gas
c) Intensity of sound waves only
d) Amplitude and frequency of sound
Answer: b
Clarification: The velocity of sound in a gas depends on the density and elasticity of the gas.
9. A 5.5 metre length of string has a mass of 0.035kg. If the tension in the string in 77N, the speed of a wave on the string is?
a) 110m/s
b) 165m/s
c) 77m/s
d) 102m/s
Answer: a
Clarification: Here m=0.035/5.5 kg/m T=77N
v=√(T/m)=√((77×5.5)/0.035)=110m/s.
10. Standing waves are produced in 10m long stretched string. If the string vibrates in 5 segments and wave velocity in 20m/s, the frequency is?
a) 5Hz
b) 10Hz
c) 2Hz
d) 4Hz