Question 23.CA.3: Properties of a refracted wave A monochromatic beam of light...
Properties of a refracted wave
A monochromatic beam of light passes from air into a block of clear plastic. Which statement correctly describes the changes in the properties of the light as it enters the glass?
A. The frequency of the light and the speed at which it travels remain the same, but the wavelength of the light decreases.
B. Both the wavelength of the light and the speed at which it travels decrease, but the frequency of the light remains the same.
C. Both the frequency of the light and the speed at which it travels decrease, but the wavelength of the light increases.
As the definition of the index of refraction indicates, light travels with a speed of c only when it is traveling through vacuum. As it travels through any other medium, light travels with a speed less than c, and the greater the index of refraction of the medium, the slower light travels. Therefore, as the beam of light goes from air to glass, the speed of the wave must decrease. As we’ve noted, the frequency cannot change when the wave crosses an interface because that would necessitate creating or destroying waves at the interface. Traveling at a slower speed with the same frequency means that the wavelength of the light must decrease. Therefore, the correct answer is B.