Question

When a ray of light is refracted, the refracted ray does not have the same wavelength as the incident ray. Which of the following explain this phenomenon?
I. Some of the energy of the incident ray is carried away by the reflected ray
II. The boundary surface absorbs some of the energy of the incident ray
III. The incident and refracted rays do not travel with the same velocity

• A. I only
• B. II only
• C. III only
• D. I and II only
• E. I, II, and III

Answer 1

The correct option is C III only

Statement I is true, but it doesnt explain why a refracted ray should have a different wavelength. The fact that some of the incident ray is reflected means that the refracted ray will have a different amplitude, but it will not affect the frequency.
Statement II is false, and even if it were true, a change in energy would affect the frequency of the wave, not its wavelength.
Statement III correctly explains why refracted rays have different wavelengths from their incident rays. A light ray will maintain the same frequency, and hence color, when it is refracted. However, since the speed of light differs in different substances, and since the wavelength is related to the speed of light, v, by the formula $\lambda =\frac{v}{f}$ a change in the speed of light will make a change in the wavelength as well.