Question

Why do we need a prism for dispersion of light?

Answer 1

Hint: In order to solve this question, we are going to first define the dispersion of light, then, the case of a prism is discussed and explained how the dispersion of light is taking place. We will also tell the factors on which the dispersion of light depends and what changes to the light ray it causes.

Complete step-by-step solution:
Dispersion is defined as the phenomena of splitting of light into its component colors. A prism is designed in such a way that the two faces are not parallel to each other. Now when a light ray passes through an interface of the two medias having different refractive indices, it gets bent and the direction depends on whether the ray is travelling from denser to the rarer medium or vice versa. In case of travelling from the rarer to the denser medium, the ray bends towards the normal and its speed decreases and increases in case it travels from denser to the rarer medium.
Now, in a visible light, the different components have different wavelengths thus, the change in the speed for each color will be different while travelling from the prism’s other face to the outer surface. Hence, all the colors get separated from each other at different speeds. Hence, the dispersion of the light occurs in the prism.

Note: It is important to note that this phenomenon of the dispersion of the light can’t happen in a glass slab or other surfaces because the slab has parallel faces due to which no dispersion takes place. The light rays travel a very small distance from the first interface to reach over to the second interface and emerge.