Class 10 CBSE Science – Human Eye and
the Colourful World
Quick idea: This chapter is basically the story of how our eyes form images and why light does
all those dramatic things in nature—rainbows, blue skies, red sunsets and colourful effects.
1. The Human Eye
The human eye is a natural optical instrument. It works somewhat like a camera: light enters the
eye, gets focused, and forms an image on the retina. The brain then interprets this image.
Cornea – The transparent front surface of the eye. Most of the refraction of incoming light
occurs here.
Iris – The coloured part of the eye. It controls the size of the pupil.
Pupil – The small opening through which light enters the eye. It becomes smaller in bright light
and larger in dim light.
Eye lens – A transparent, flexible convex lens that fine-tunes the focus of light on the retina.
Ciliary muscles – Muscles that change the curvature and therefore the focal length of the eye
lens.
Retina – A light-sensitive layer where the image is formed. It contains photoreceptor cells.
Optic nerve – Carries visual information from the retina to the brain.
2. Power of Accommodation
The ability of the eye lens to change its focal length so that objects at different distances can be
focused clearly on the retina is called accommodation.
For a nearby object: ciliary muscles contract → lens becomes thicker/more curved → focal
length decreases.
For a distant object: ciliary muscles relax → lens becomes thinner/less curved → focal length
increases.
3. Near Point and Far Point
For a normal adult eye:
the Colourful World
Quick idea: This chapter is basically the story of how our eyes form images and why light does
all those dramatic things in nature—rainbows, blue skies, red sunsets and colourful effects.
1. The Human Eye
The human eye is a natural optical instrument. It works somewhat like a camera: light enters the
eye, gets focused, and forms an image on the retina. The brain then interprets this image.
Cornea – The transparent front surface of the eye. Most of the refraction of incoming light
occurs here.
Iris – The coloured part of the eye. It controls the size of the pupil.
Pupil – The small opening through which light enters the eye. It becomes smaller in bright light
and larger in dim light.
Eye lens – A transparent, flexible convex lens that fine-tunes the focus of light on the retina.
Ciliary muscles – Muscles that change the curvature and therefore the focal length of the eye
lens.
Retina – A light-sensitive layer where the image is formed. It contains photoreceptor cells.
Optic nerve – Carries visual information from the retina to the brain.
2. Power of Accommodation
The ability of the eye lens to change its focal length so that objects at different distances can be
focused clearly on the retina is called accommodation.
For a nearby object: ciliary muscles contract → lens becomes thicker/more curved → focal
length decreases.
For a distant object: ciliary muscles relax → lens becomes thinner/less curved → focal length
increases.
3. Near Point and Far Point
For a normal adult eye:
