Question

A beam of white light passing through a prism is split into constituent colours the light which undergoes least deviation is
A. Violet
B. Yellow
C. Red
D. green

Answer 1

Hint: When the white light got separated into its constituent colours, the angle of deviation is maximum for the colour having shorter wavelength and it is minimum for the colour having higher wavelength. For calculating the angle of deviation, you have to remember the concept of VIBGYOR.

Complete answer:
As we all know, when white light passes through the prism, it gets separated into its component colours that are violet, indigo, blue, green, yellow, orange and red, which is also known as VIBGYOR. The process of separation of white light into its constituent colours is called dispersion of light.

Angle of deviation:It is defined as the angle that is 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 $ and is given by
$\theta = \left( {\mu - 1} \right)A$
Here, $\mu $ is the refractive index of the prism and $A$ is the angle of the prism. Therefore, we can say that the angle of deviation is dependent on the refractive index of the prism.

Refractive index of the prism is given by
$\mu = A + \dfrac{B}{{{\lambda ^2}}} + \dfrac{C}{{{\lambda ^4}}} + ....$
Therefore, refractive index is inversely proportional to the wavelength of the light.Hence, in the visible light spectrum, the colours having shorter wavelength will have high refractive index and the colour having high wavelength will have low refractive index. Now, the red light has maximum wavelength and violet light has minimum wavelength, therefore, the refractive index of the red light will be minimum and the refractive index of violet light will be maximum.

Hence, the red light will be least deviated when it passes from the prism. Thus, (C) is the correct option.

Note: The light will get separated into its constituent colours because of the fact that different colours of light travels at different speeds and also the refractive index is different for different colours. As a result, when a white light will pass through the prism, the components of light will bend into different colours.