Question

When light is refracted into a medium,
(a) its wavelength and frequency increase
(b) its wavelength increases but frequency remains unchanged
(c) its wavelength decreases but frequency remains unchanged
(d) its wavelength and frequency decrease

Answer 1

(c) its wavelength decreases but frequency remains unchanged

Frequency of a light wave, as it travels from one medium to another, always remains unchanged, while wavelength decreases.

Decrease in the wavelength of light entering a medium of refractive index $\mu$ is given by
$$\begin{gathered} {\lambda }_{{\rm M}}=\frac{\lambda }{\mu }, \\ where{\lambda }_{{\rm M}}=wavelengthinmedium \\ \lambda =wavelengthinvacuum \\ \mu =refractiveindex \end{gathered}$$