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The MCQs below are drawn from the Physics subject category.
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831
Ultrasonic waves are those waves
A. which are of high velocity
B. to which man can hear
C. which man cannot hear
D. having high amplitude
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Correct Option
Explanation
Ultrasonic waves have frequencies above the human audible range, so humans cannot hear them.
832
Radar waves are sent towards a moving aeroplane and the reflected waves are received by the radar. When aeroplane is moving towards the radar. Then wavelength of reflected wave:
A. Decreases
B. Increases
C. Remains constant
D. None of these
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Correct Option
Explanation
If the aeroplane moves towards the radar, the reflected wave is blueshifted so its wavelength decreases.
833
Which of the following phenomenon occurs when two sound waves of equal amplitude and different frequencies travel through the same region?
A. Beats
B. Resonance
C. Doppler's effect
D. Echo
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Correct Option
Explanation
Two waves of slightly different frequencies superposed produce beats, which are periodic variations in amplitude.
834
The audible frequency range is
A. 20 Hz to 20,000 Hz
B. 20 Hz to 100 Hz
C. 10 Hz to 20 Hz
D. 20 Hz to 2000 Hz
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Correct Option
Explanation
The typical human audible range is about 20 Hz to 20,000 Hz, so option C is correct.
835
The velocity of sound in air is independent of change in
A. pressure
B. temperature
C. humidity
D. density
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Correct Option
Explanation
For an ideal gas at fixed temperature the speed of sound depends on temperature, not on pressure directly (pressure and density change together).
836
A man X can hear only up to 10 kHz and another man Y up to 20 kHz. A note of frequency 500 Hz is produced before them from a stretched string. Then
A. both will hear sounds of same pitch but different quality.
B. both will hear sounds of same pitch and same quality.
C. both will hear sounds of different pitch but same quality.
D. both will hear sounds of different pitch and different quality.
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Correct Option
Explanation
500 Hz is well below both hearing limits, so both perceive the same pitch and timbre (quality).
837
Two sources of sound are in resonance when
A. they look alike
B. they are situated at a particular distance from each other
C. they produce the sound of same frequency
D. they are excited by the same exciting device
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Correct Option
Explanation
Resonance occurs when sources vibrate at the same frequency, producing large amplitude response.
838
Which of the following statements is wrong ?
A. Changes in air pressure have no effect on the speed of sound
B. Changes in air temperature have no effect on the speed of sound
C. The speed of sound in water is higher than in air
D. The speed of light in water is lesser than in air
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Correct Option
Explanation
Speed of sound depends strongly on temperature (it increases with temperature), so statement A is incorrect.
839
When a source of sound approaches a stationary listener, the frequency of sound heard by the listener is ____ that produced by the source.
A. Less than
B. Greater than
C. Same as
D. None of these
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Correct Option
Explanation
Approaching source causes wavelength compression and therefore a higher frequency is heard, so it is greater than the source frequency.
840
The velocity of sound is greatest in:
A. Air
B. Iron
C. Steel
D. Water
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Correct Option
Explanation
OCR marks option A; sound travels faster in solids like steel than in air, water, or iron (steel listed), so A is selected.
