Question

How does the speed of light in glass change on increasing the wavelength of light?
A. Increases
B. Decreases
C. Remains constant
D. Data insufficient

Answer 1

Hint: In a medium speed of light is constant. So, both frequency and the wavelength will also be constant. But if light ray moves from one medium to another medium the velocity of the light will change due to change in the refractive index of the medium. But frequency of light will still be constant, so the wavelength will be varying with velocity.

Complete Step-by-Step solution:
For electromagnetic waves or light, the frequency of light will remain constant. The frequency will not change.
Now, the relation between the speed of light, wavelength of the light and the frequency can be expressed as,
$v=\nu \lambda $
Where, v is the speed of light, $\lambda $ is the frequency of light and $\nu $ is the frequency of light.
Now, when the light enters the glass, the frequency of light will remain constant. So, speed of light will be directly proportional to the wavelength of light.
$v\propto \lambda $
So, as the speed of light will change the wavelength of light will also change or vice versa.
So, on increasing the wavelength of light in glass, the velocity of light will also increase.
The correct option is (A).

Note: When waves travel from a rarer medium to a denser medium, velocity of the wave will decrease. But the frequency remains the same, so the wavelength of the light decreases with it.
When the light travels from a denser to a rarer medium the velocity of the light wave will increase and with it the wavelength of the light will also increase.
At vacuum the wavelength of a light will be the largest.