Q. A car moving at 30 m/s emits a sound of frequency 500 Hz. What frequency does an observer standing still hear as the car approaches?
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A.
500 Hz
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B.
550 Hz
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C.
600 Hz
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D.
650 Hz
Solution
Using the Doppler effect formula, f' = f(v + vo) / (v - vs), where v = 340 m/s, vo = 0, vs = 30 m/s, f' = 500(340)/(340 - 30) = 500(340/310) ≈ 548 Hz.
Correct Answer:
C
— 600 Hz
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Q. A sound source is moving away from an observer. If the source emits a sound of frequency 400 Hz, what frequency does the observer hear?
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A.
Less than 400 Hz
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B.
Exactly 400 Hz
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C.
More than 400 Hz
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D.
Infinity
Solution
As the source moves away, the frequency decreases, so the observer hears a frequency less than 400 Hz.
Correct Answer:
A
— Less than 400 Hz
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Q. If a sound source is moving away from a stationary observer, which of the following describes the observed frequency?
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A.
Higher than the source frequency
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B.
Lower than the source frequency
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C.
Equal to the source frequency
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D.
Variable depending on distance
Solution
The observed frequency decreases as the source moves away, due to the Doppler effect.
Correct Answer:
B
— Lower than the source frequency
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Q. If a sound wave travels from air into water, how does its speed change?
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A.
Increases
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B.
Decreases
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C.
Remains the same
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D.
Becomes zero
Solution
The speed of sound increases when it travels from air (approximately 343 m/s) into water (approximately 1482 m/s).
Correct Answer:
A
— Increases
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Q. If a source of sound is moving towards a stationary observer, what happens to the frequency of the sound heard by the observer?
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A.
It decreases
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B.
It remains the same
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C.
It increases
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D.
It becomes zero
Solution
According to the Doppler effect, if the source is moving towards the observer, the frequency increases.
Correct Answer:
C
— It increases
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Q. In the Doppler effect, what happens to the frequency of a sound wave as the source moves towards the observer?
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A.
It decreases
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B.
It remains the same
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C.
It increases
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D.
It becomes zero
Solution
As the source moves towards the observer, the waves are compressed, leading to an increase in frequency.
Correct Answer:
C
— It increases
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Q. What effect does temperature have on the speed of sound in air?
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A.
Increases with temperature
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B.
Decreases with temperature
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C.
No effect
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D.
Depends on humidity
Solution
The speed of sound in air increases with an increase in temperature.
Correct Answer:
A
— Increases with temperature
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Q. What happens to the wavelength of a sound wave as its frequency increases, assuming the speed of sound remains constant?
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A.
Wavelength increases
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B.
Wavelength decreases
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C.
Wavelength remains constant
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D.
Wavelength becomes zero
Solution
If the speed of sound is constant, an increase in frequency results in a decrease in wavelength.
Correct Answer:
B
— Wavelength decreases
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Q. What is the formula for the observed frequency (f') in the Doppler effect when the source is moving towards a stationary observer?
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A.
f' = f (v / (v - vs))
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B.
f' = f (v + vs) / v
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C.
f' = f (v - vs) / v
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D.
f' = f (v / (v + vs))
Solution
The formula for the observed frequency when the source is moving towards the observer is f' = f (v / (v - vs)).
Correct Answer:
A
— f' = f (v / (v - vs))
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Q. What is the frequency of a sound wave if its wavelength is 2 meters and the speed of sound is 340 m/s?
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A.
170 Hz
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B.
340 Hz
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C.
680 Hz
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D.
850 Hz
Solution
Frequency (f) = Speed (v) / Wavelength (λ) = 340 m/s / 2 m = 170 Hz.
Correct Answer:
B
— 340 Hz
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Q. What is the primary reason for the Doppler effect in sound waves?
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A.
Change in amplitude
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B.
Change in wavelength
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C.
Change in speed
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D.
Change in medium
Solution
The Doppler effect is primarily due to the change in wavelength as the source moves relative to the observer.
Correct Answer:
B
— Change in wavelength
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Q. What is the relationship between frequency and wavelength in a sound wave?
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A.
Directly proportional
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B.
Inversely proportional
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C.
No relationship
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D.
Depends on amplitude
Solution
Frequency and wavelength are inversely proportional; as frequency increases, wavelength decreases.
Correct Answer:
B
— Inversely proportional
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Q. What is the relationship between frequency and wavelength in sound waves?
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A.
Directly proportional
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B.
Inversely proportional
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C.
No relationship
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D.
Depends on medium
Solution
Frequency and wavelength are inversely proportional; as frequency increases, wavelength decreases.
Correct Answer:
B
— Inversely proportional
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Q. Which of the following scenarios would result in a higher pitch sound being heard?
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A.
Source moving away from observer
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B.
Source moving towards observer
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C.
Observer moving away from source
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D.
Observer moving towards source
Solution
A higher pitch sound is heard when the source is moving towards the observer, compressing the sound waves.
Correct Answer:
B
— Source moving towards observer
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