Question

exam lesson name: light and sound
exam number: 700699rr
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question 18 of 20 :
select the best answer for the question.

1. if a source of sound waves is rapidly approaching a person, the sound heard by the person appears to have

○ a. a pitch lower than the original pitch.
○ b. a period higher than the original period.
○ c. an amplitude lower than the original amplitude.
○ d. a frequency higher than the original frequency.
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Explanation:

This question is about the Doppler effect for sound waves. When a sound source approaches an observer, the observed frequency increases (and pitch, related to frequency, also increases). Let's analyze each option:

• Option A: When approaching, pitch should be higher, not lower. Eliminate A.
• Option B: Period is inversely related to frequency ($T = \frac{1}{f}$). If frequency increases, period decreases, so period can't be higher. Eliminate B.
• Option C: Amplitude relates to loudness, not the Doppler effect (which is about frequency/pitch). The Doppler effect doesn't change amplitude in this context. Eliminate C.
• Option D: Due to the Doppler effect, as the source approaches, the observed frequency is higher than the original. This matches.

Answer:

D. a frequency higher than the original frequency.