Question

When the light enters from air to glass, which colour the angle of deviation maximum?
A) Red
B) Yellow
C) Blue
D) Violet

Answer 1

Hint: Just remember, when white light passes through the prism, the angle of deviation is maximum for the colour having shorter wavelength and it is minimum for the colour having larger wavelength. For remembering the wavelength of colours, you have to remember the concept of VIBGYOR.

Complete step by step answer:
As we all know, when white light is passed through prism, it gets separated into its component colours i.e. violet, indigo, blue, green, yellow, orange and red, which is also known as VIBGYOR. The process of separation of white light into its component colours is called dispersion of light.
Now, here a question might arise, why light gets separated into different colours after passing through prism?
This is because of the fact that different colours of light travel at different speeds and also the refractive index is different colours. As a result, when a white light is passed through the prism, the components of light bend into different colours. Hence, it causes a single beam of light to separate into colours.

ANGLE OF DEVIATION: It is defined as the angle obtained by the difference between angle of incidence and angle of refraction, when light passes through the prism. Angle of deviation is denoted as $\theta $.
In the visible light spectrum, the colours having shorter wavelength will be deviated more from their original than the colours having shorter wavelength.
As we know, when we move from violet light to red light in VIBGYOR, the wavelength goes on decreasing.
Therefore, violet will face more deviation than that of red light.
Hence, when light goes from air to glass, violet colour has a maximum angle of deviation.
Thus, (D) is the correct option.

Additional Information:
Formation of a rainbow is a good example of dispersion of light.
Water in water droplets has a refractive index that enables the light to refract. When sunlight passes through the water droplets, it refracts the light and the light is spread into its constituent colours through dispersion of light.
We all know, rainbow patterns are made up of seven colours. You will notice that red will be at the bottom and violet colour will be at top of the rainbow. This is because red light has higher wavelength so it is least deviated and violet colour has lower wavelength so it is most deviated.

Note: Now, you might get confused about angle of deviation and angle of prism. Just remember, angle of deviation is directly proportional to the angle of the prism. Therefore, angle of deviation increases with increase in angle of prism.