Human Eye and Colourful World

Chapter Summary

Human Eye

Cornea, iris, lens and retina are the main parts of the human eye.

Image is formed on retina.

Optic nerves carry signals from retina to the brain.

Power of Accommodation

The ability of eye to clearly see both near and distant objects is called the power of accommodation.

25 cm is the minimum distance for clear vision.


A myopic person is unable to clearly see distant object.

This vision defect is corrected by using a concave lens.


A hypermetropic person is unable to clearly see nearby object.

This vision defect s corrected by using a convex lens.


The cornea becomes cloudy due to deposition of debris.

Cataract is corrected by surgery and by implantation of artificial lens.

Dispersion of Light

Splitting of white light into its component colurs is called dispersion of light.

When white light passes through a prism, a band of rainbow-like colours is formed.

Formation of Rainbow

When ray of light passes through raindrops, it undergoes refraction, dispersion and internal reflection.

Thus rainbow is formed due to refraction, dispersion and internal reflection of light.

Twinkling of Stars

Light from stars undergoes a series of refraction when it passes through different layers of atmosphere.

Due to this, the apparent position of star keeps on changing and we get to see twinkling of stars.

Sunrise and Sunset

Sun appears 2 minute before actual sunrise and remains visible 2 minutes after actual sunset.

It happens because red light travels the farthest due to atmospheric refraction.

Scattering of Light

When ray of light hits a particle, light is scattered in different directions.

Scattering of light happens because of non-uniformity of particles.

Tyndall Effect

When light travels through a colloid, it appears like a visible beam of light.

This is called Tyndall effect.

It happens when particles of medium are smaller or equal to the wavelength of visible spectrum.

Blue Colour of Sky

Size of particles in air is smaller than the wavelength of visible spectrum.

Hence, these particles scatter light of shorter wavelength more efficiently than light of longer wavelength.

Blue colour is scattered the most and hence the sky appears blue during the day.