Dispersion of Light

 

Light when passes through prism split into different color components. This phenomena is called dispersion of light. A prism is a transparent glass having two plane surfaces inclined at an angle. White light beam passing through prism split into seven colors – “violet, indigo blue, green, yellow orange and red”. The band of colors which is dispersed from light entering in glass prism is called as spectrum.

Reason Behind Dispersion of Light

White light consist of different color components. Different colors travel with different speed in the glass prism, in this way different colors undergo bends with different angles. Slower the speeds in the glass make the light bend more. And so violet light bend the most and red light bend the least. Each color emerge out independently with different angle thus producing the spectrum of light.

Color components in sunlight

Isaac Newton took two identical prisms. He placed one vertically upward and second vertically downward such that light emitting from one will fall on second prism. Newton allowed a beam of sunlight i.e. white beam to fall on first prism. So he got seven different colors i.e. white beam split into different colors. These colors then fall on second prism and thus the he got beam of white again. Based on this He concluded that sunlight is made of seven colors.

Rainbow

After rain shower we observe rainbow in the sky. It is due to combined effects of refraction, reflection and dispersion of light. A tiny water droplet act as a small prism. Incident light when fall on a tiny droplet first get refracted inside the droplet. While travelling inside the droplet, light beam undergoes dispersion. The dispersed light get reflected back at the boundary of the droplet due to total internal reflection. When it emerge out of the droplet again it undergoes refraction. The combined effect of infinite number of such droplets, produces rainbow in the sky.

Recombination of spectrum of colours

A spectrum of seven colours of lights can be recombined to form back white light. This can be done by placing two glass prisms side by side. But, place the second glass prism in an inverted position. When white light passes through first prism it disperses the light into seven colours and when this beam of light enters the second prism which is placed in an inverted position, a white light is obtained when it comes out of the second prism.

The seven coloured lights recombine to form white light due to second glass prism which is placed in a reversed position.