SAT Subject Physics Practice Question 301: Answer and Explanation
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?
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