Chapter 11: The Human Eye and the
Colourful World
🌟 1. Structure and Working of the Human Eye
The human eye is a natural optical instrument that helps us see objects
around us.
Parts of the Eye and Their Functions
Part Function
Transparent, curved front part of the eye. It refracts most of
Cornea
the light rays entering the eye.
Aqueous Transparent fluid between cornea and lens; maintains
Humour pressure and provides nutrients to the eye.
Colored circular membrane behind the cornea; controls the
Iris
size of the pupil.
Dark circular opening in the center of the iris; regulates the
Pupil
amount of light entering the eye.
Transparent, convex, and flexible structure that focuses light
Lens
on the retina.
Ciliary Control the curvature and focal length of the lens (help in
Muscles focusing).
Light-sensitive layer at the back of the eye containing rods
Retina and cones. Image formed here is real, inverted, and
smaller.
Rods and Rods detect brightness (black and white), Cones detect
Cones color.
Optic
Carries visual information from the retina to the brain.
Nerve
Vitreous Jelly-like fluid filling the space between lens and retina;
Humour maintains the shape of the eyeball.
👁️
2. Power of Accommodation
, The ability of the eye lens to adjust its focal length to clearly see
objects at different distances.
Distant objects: Ciliary muscles relax → lens becomes thinner →
focal length increases.
Nearby objects: Ciliary muscles contract → lens becomes thicker →
focal length decreases.
Limits of Vision
Near Point: The closest distance at which the eye can see clearly =
25 cm (for a normal eye).
Far Point: The farthest distance at which the eye can see clearly =
Infinity.
⚠️
3. Defects of Vision and Their Correction
(i) Myopia (Short-sightedness)
Defect: Can see nearby objects clearly but not distant ones.
Cause:
o Eye ball too long
o Lens too curved (short focal length)
Image Formation: Image forms in front of the retina.
Correction: Use a concave (diverging) lens to diverge the light
rays.
(ii) Hypermetropia (Long-sightedness)
Defect: Can see distant objects clearly but not nearby ones.
Cause:
o Eye ball too short
o Lens too thin (long focal length)
Image Formation: Image forms behind the retina.
Correction: Use a convex (converging) lens to converge the
light rays before entering the eye.
Colourful World
🌟 1. Structure and Working of the Human Eye
The human eye is a natural optical instrument that helps us see objects
around us.
Parts of the Eye and Their Functions
Part Function
Transparent, curved front part of the eye. It refracts most of
Cornea
the light rays entering the eye.
Aqueous Transparent fluid between cornea and lens; maintains
Humour pressure and provides nutrients to the eye.
Colored circular membrane behind the cornea; controls the
Iris
size of the pupil.
Dark circular opening in the center of the iris; regulates the
Pupil
amount of light entering the eye.
Transparent, convex, and flexible structure that focuses light
Lens
on the retina.
Ciliary Control the curvature and focal length of the lens (help in
Muscles focusing).
Light-sensitive layer at the back of the eye containing rods
Retina and cones. Image formed here is real, inverted, and
smaller.
Rods and Rods detect brightness (black and white), Cones detect
Cones color.
Optic
Carries visual information from the retina to the brain.
Nerve
Vitreous Jelly-like fluid filling the space between lens and retina;
Humour maintains the shape of the eyeball.
👁️
2. Power of Accommodation
, The ability of the eye lens to adjust its focal length to clearly see
objects at different distances.
Distant objects: Ciliary muscles relax → lens becomes thinner →
focal length increases.
Nearby objects: Ciliary muscles contract → lens becomes thicker →
focal length decreases.
Limits of Vision
Near Point: The closest distance at which the eye can see clearly =
25 cm (for a normal eye).
Far Point: The farthest distance at which the eye can see clearly =
Infinity.
⚠️
3. Defects of Vision and Their Correction
(i) Myopia (Short-sightedness)
Defect: Can see nearby objects clearly but not distant ones.
Cause:
o Eye ball too long
o Lens too curved (short focal length)
Image Formation: Image forms in front of the retina.
Correction: Use a concave (diverging) lens to diverge the light
rays.
(ii) Hypermetropia (Long-sightedness)
Defect: Can see distant objects clearly but not nearby ones.
Cause:
o Eye ball too short
o Lens too thin (long focal length)
Image Formation: Image forms behind the retina.
Correction: Use a convex (converging) lens to converge the
light rays before entering the eye.
