SAT Subject Physics Practice Question 112: Answer and Explanation

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Question: 112

7. A sound wave travels through a metal rod with wavelength λ and frequency f. Which of the following best describes the wave when it passes into the surrounding air?

Wavelength      Frequency

A. Less than λ      Equal to f
B. Less than λ      Less than f
C. Greater than λ      Equal to f
D. Greater than λ      Less than f
E. Greater than λ      Greater than f

Correct Answer: A

Explanation:

In general, sound travels faster through solids than through gases. Therefore, when the wave enters the air from the metal rod, its speed will decrease. The frequency, however, will not change. Since v = λf must always be satisfied, a decrease in v implies a decrease in λ.

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