Dispersion of White Light

Dispersion of White Light

Understanding Dispersion

• White light is made up of a spectrum of colours — the same colours seen in a rainbow.
• These colours include red, orange, yellow, green, blue, indigo, and violet.
• Dispersion is the process where white light is separated into its constituent colours.
• The dispersion of light occurs when different colours of light bend by different amounts upon passing through a medium. This bending of light is called refraction.
• The amount of bending (refraction) depends on the wavelength or colour of the light.

Dispersion through a Prism

• When white light passes through a prism, it splits into its spectrum of colours.
• This happens because the prism refracts (bends) the different colours by different amounts.
• Violet light refracts the most and red light the least.
• This results in the white light spreading out into a spectrum of colours.

Understanding Rainbows

• A rainbow is a natural example of the dispersion of white light.
• It is formed when sunlight (white light) is refracted, or bent, and then reflected by raindrops.
• The light is refracted once as it enters the raindrop, reflected from the inside surface of the raindrop, and then refracted again as it leaves the raindrop.
• This two-step refraction causes the sunlight to spread out into its spectrum of colours.

Applications of Dispersion

• The dispersion of white light is used in many real-world applications.
• Optical prisms can be used to separate white light into its constituent colours, a principle that forms the basis of spectrum analysis in fields such as astronomy and chemical analysis.
• Spectroscopes use diffraction gratings and prisms to produce and analyse spectra.
• CDs and DVDs use the principle of light dispersion to store and read digital data.

Key Points to Remember

• The colours of white light, in increasing degree of refraction, are red, orange, yellow, green, blue, indigo, and violet.
• Refraction is the reason behind both lenses focusing light and prisms dispersing light.
• The colour spectrum seen in a rainbow is not due to reflection, but due to dispersion by the process of refraction.