Sound and its application

PAPhysicsScience

Engineering Physics Questions and Answers – Sounds and Waves – 1

This set of Engineering Physics Multiple Choice Questions & Answers (MCQs) focuses on “Sounds and Waves – 1”.

1. Statement: Ocean waves hitting a beach are always found to be nearly normal to the shore.
Reason: Once waves hitting a beach are assumed to be plane waves.
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
View Answer

Answer: a
Explanation: Both the statement and reason are true. Once waves are transverse in nature, they hit the shore normally. As these waves spread out, their radius of curvature becomes so large that they may be considered as plane waves.

2. Statement: When a beetle moves along the sand within a few tens of centimetres of a sand scorpion, the scorpion immediately turns towards the beetle and dashes towards it.
Reason: When a beetle disturbs the sand, it sends pulses is longitudinal, while the other set in transverse.
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
View Answer

Answer: a
Explanation: Both the statement and reason are true. A beetle’s motion sends fast longitudinal and slower transverse waves along sand’s surface. The sand scorpion intercepts the longitudinal waves first and senses the direction of the beetle by noting which are of the eight legs of the scorpion is disturbed first by the pulses. Then the scorpion dashes towards the beetle to catch it

3. Statement: When two vibration tuning forks having frequencies 256Hz and 512Hz are held near each other, beats cannot be heard.
Reason: The principle of superposition is valid if the frequencies of the oscillators are nearly equal.
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
View Answer

Answer: c
Explanation: The statement is true but the reason is false. The beats can be heard only if the two sounds do not exceed 10Hz.

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) 20m/s
b) 40m/s
c) 5m/s
d) 10m/s
View Answer

Answer: a
Explanation: Since a node is formed at the fixed end, so
ʎ/2=10cm or ʎ=20cm
γ=100Hz
v=ʎγ=100×0.20=20m/s.

5. A vehicle, with a horn of frequency n is moving with a velocity of 30m/s in a direction perpendicular to the straight line joining the observer and the vehicle. The observer perceives the sound to have a frequency n+n₁. Then (if the sound velocity in air is 300m/s)
a) n₁=0.1n
b) n₁=0
c) n₁=10n
d) n₁=-0.1n
View Answer

Answer: b
Explanation: As the vehicle moves in a direction perpendicular to the line joining the observer and the vehicle, the component of the velocity along this direction zero. There is no Doppler effect and the frequency of sound remains unchanged.

6. Lights can travel in a vacuum but not sound, because ______________
a) Speed of sound is very slow than light
b) Light waves are electromagnetic in nature
c) Sound waves are electromagnetic in nature
d) Light waves are not electromagnetic in nature
View Answer

Answer: a
Explanation: Light can travel in a vacuum because light waves are electromagnetic in nature.

7. Velocity of sound in air is ___________
a) Faster in dry air than in moist air
b) Directly proportional to temperature
c) Directly proportional to pressure
d) Slower in dry air than in moist air
View Answer

Answer:b
Explanation: Velocity of sound is proportional to temperature. It is independent of pressure and increases with humidity.

8. When sound travels from air to water, which parameter does not change?
a) Wavelength
b) Frequency
c) Velocity
d) Temperature
View Answer

Answer: b
Explanation: Frequency remains unchanged when sound travels from air to water.

9. The apparent frequency in Doppler’s effect does not depend upon ___________
a) Speed of the observer
b) Distance between the observer and source
c) Speed of the source
d) Frequency of the source
View Answer

Answer: b
Explanation: Apparent frequency in Doppler’s effect depends on frequency of source, direction and velocity of source and observer. It does not depend on the distance between observer and source.

10. In a sinusoidal wave, the time required for a particular point to move from maximum displacement to zero displacement is 0.107sec. The frequency of wave is?
a) 0.73Hz
b) 0.36Hz
c) 1.47Hz
d) 2.94Hz
View Answer

Answer: c
Explanation: Time taken in moving from maximum displacement to zero displacement is
T/4=0.170s or T=0.68s
Frequency,
v=1/T=1/0.67=1.47Hz.

11. Wave has simple harmonic motion whose period is 4seconds while another wave which also possesses simple harmonic motion has its period 3sec. If both are combined, then the resultant wave will have the period equal to ___________
a) 4sec
b) 5sec
c) 12sec
d) 3sec
View Answer

Answer: c
Explanation: On superposition of the two waves, beats are produced.
Beat frequecny=1/T₂ -1/T₁ = 1/3-1/4=1/12
Time period=12seconds.

Sanfoundry Global Education & Learning Series – Engineering Physics.