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The MCQs below are drawn from the Physics subject category.
Showing 841–850
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841
Sonar is a machine for position and ranging
A. Aircrafts
B. Submarines
C. Missiles
D. None of these
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Explanation
SONAR (sound navigation and ranging) is primarily used underwater for detecting and ranging submarines and other underwater objects.
842
When a sound source moves towards a stationary observer, there is
A. an apparent increase in wavelength
B. an apparent decrease in frequency
C. a change in the velocity of the sound
D. an apparent increase in frequency
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Explanation
Due to the Doppler effect, a source moving toward an observer produces a higher observed frequency (apparent increase).
843
The noise of a danger signal to the west of you is transmitted to your ear by air ______.
A. Vibrating in a west-south direction
B. Vibrating in a west-east direction
C. Vibrating in a west-north direction
D. None of these
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Explanation
Sound from the west involves air oscillations along the line between source and listener (west–east direction).
844
On which characteristic does the loudness of sound depend upon?
A. Pitch
B. Amplitude
C. Wavelength
D. Speed
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Explanation
Loudness is related to the amplitude (intensity) of the sound wave; greater amplitude yields greater loudness.
845
Longitudinal waves do not exhibit:
A. Refraction
B. Polarization
C. Reflection
D. Diffraction
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Explanation
Longitudinal waves, like sound, cannot be polarized because polarization is a property of transverse wave oscillations.
846
The source of sound generating a frequency of 3 kHz recedes from an observer with a speed of 0.5 times the speed of sound in air. The frequency heard by the observer is
A. 4 kHz
B. 2 kHz
C. 1 kHz
D. 6 kHz
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Explanation
For receding source f' = f/(1 + v_s/v) = 3000/(1 + 0.5) = 3000/1.5 = 2000 Hz (2 kHz).
847
4. A siren emitting a sound of frequency 800 Hz moves away from an observer towards a cliff at a speed of 15 ms^-1. Then, the frequency of sound that the observer hears in the echo reflected from the cliff is (Take velocity of sound in air = 330 ms^-1).
A. 885 Hz
B. 838 Hz
C. 800 Hz
D. 765 Hz
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Explanation
The cliff receives frequency f' = f·v/(v - v_s) = 800·330/(330-15) ≈ 838 Hz, and the reflected sound of that frequency is heard by the observer.
848
With the increase of temperature, the pitch of an organ pipe
A. decreases
B. increases
C. remains the same
D. may increase or decrease
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Explanation
Raising temperature increases the speed of sound, which increases the frequency for a given pipe length, thus raising the pitch.
849
When temperature increases, frequency of an organ pipe
A. decreases
B. remains the same
C. becomes zero
D. increases
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Explanation
Raising temperature increases the speed of sound in air, increasing the resonant frequency of an organ pipe.
850
Define Mach Number.
A. It is the ratio of the velocity of sound to the velocity of an object
B. It is the ratio of the strain to the stress
C. It is the ratio of the velocity of an object to the velocity of sound
D. It is the ratio of the stress to the strain
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Explanation
Mach number is defined as the ratio of an object's speed to the speed of sound in the medium.
