Question

When a light ray enters in a glass slab from air then:
A) Its wavelength increases.
B) Its wavelength decreases.
C) Its frequency increases.
D) Neither wavelength or frequency changes.

Answer 1

Hint: As we know, when a light enters into a glass slab it bends towards the normal this phenomena is commonly called refraction. We know that refraction is due to the change in wavelength due to change in speed of light in other medium while frequency is inherent property of a light ray.

Complete step by step solution:We know that glass is denser medium than air. Glass has a higher refractive index than air. So the speed of light in air is greater than the speed of light in glass. Because the relation between refractive index of glass and speed of light is
$v=\dfrac{c}{\mu }$, Where, $v$ is the speed of light at any medium, $\mu $ is the refractive index of that medium, and $c$ is the speed of light in vacuum. So, due to the higher refractive index of glass the speed of light in glass is slow.
And there is also a relation between speed of light in that medium, wavelength and frequency.
i.e. $v=f\lambda $
Where, $f$ is the frequency of light ray it is inherent property and this doesn’t change with change with medium, and $\lambda $ is wavelength of light in that medium.
So, if the speed of light decreases with change in medium then wavelength of light decreases because the frequency of light is constant.

Hence, option(B) is correct.

Additional Information:
Light is refracted when it crosses the interface from air into glass in which it moves more slowly. Since the light speed changes at the interface, the wavelength of the light must change, too. The wavelength decreases as the light enters the medium and the light wave changes direction. The refractive index can be seen as the factor by which the speed and the wavelength of the radiation are reduced with respect to their vacuum values.

Note: We have to remember that refractive index of rarer is always less than refractive index of denser object. The phenomena of refraction is discovered with the particle theory of light but after it is also explained by wave theory of light. So, the terms wavelength and frequency terms are involved in refraction phenomena.