SAT Subject Physics Practice Question 301: Answer and Explanation

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Question: 301


Note: The figure is not drawn to scale.

The figure above shows a beam of light striking the surface of a piece of glass from the air.

Let n denote the index of refraction of the glass. If the incident light has a frequency of f when traveling through the air, what is the wavelength of the light when it travels through the glass?

A. fc/n
B. n/fc
C. c/f
D. nc/f
E. c/nf

Correct Answer: E


Don’t let the underlined phrase in the question throw you. When a wave enters a new medium, its frequency does not change. So if the frequency of the light was f in the air, it’s still f in the glass. Using the equation that relates wavelength, frequency, and wave speed, along with the equation v = c/n (which follows immediately from the definition of index of refraction), we find that

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