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A sound source, moving at a constant speed of 240 m s<sup>-1</sup> towards a detector, emits sound at a constant frequency - NSC Physical Sciences - Question 6 - 2018 - Paper 1
Question 6
A sound source, moving at a constant speed of 240 m s<sup>-1</sup> towards a detector, emits sound at a constant frequency. The detector records a frequency of 5 100... show full transcript
Worked Solution & Example Answer:A sound source, moving at a constant speed of 240 m s<sup>-1</sup> towards a detector, emits sound at a constant frequency - NSC Physical Sciences - Question 6 - 2018 - Paper 1
Step 1
State the Doppler effect.
Answer
The Doppler effect refers to the apparent change in frequency or pitch of sound as a result of the relative motion between the sound source and an observer (listener). As the sound source approaches the observer, the frequency increases, and as it moves away, the frequency decreases.
Step 2
Calculate the wavelength of the sound emitted by the source.
Answer
To find the wavelength ( ( \lambda ) ) of the sound emitted by the source, we use the formula:
v = f \lambda$$ where: - \( v \) is the speed of sound (340 m s<sup>-1</sup>) - \( f \) is the frequency (5 100 Hz) Rearranging the formula yields:\lambda = \frac{v}{f} = \frac{340}{5100} \approx 0.067 , \text{m} , (or , 6.7 , \text{cm})$$
Step 3
Will the frequency of the reflected sound wave detected by the sound source be EQUAL TO, GREATER THAN or SMALLER THAN 5 100 Hz?
Answer
When the sound waves are reflected back to the approaching source, the frequency of the reflected sound would be altered due to the Doppler effect again. Since the source is moving towards the detector, the reflected sound wave will have a frequency greater than 5 100 Hz. Therefore, the frequency detected by the source will be GREATER THAN 5 100 Hz.