SAT Subject Physics Practice Question 112: Answer and Explanation
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?
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
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.