HUMAN EYE AND THE COLORFUL WORLD
Vaibhav Bhai Notes
Human Eye – Sense organ that helps us
to see
(1). Located in eye sockets in skull.
(2). Diameter of Eye is 2.3 cm.
PARTS OF HUMAN EYE:
Cornea – It is the outermost, transparent
part. It provides most of the refraction
of the light.
Lens – It is composed of a fibrous, jelly
like material. Provides the focused real
and inverted image of the object on
retina. This is convex lens that
converges light at retina.
Iris – It is a dark muscular diaphragm
that controls the size of the pupil.
Pupil – It is the window of the eye. It is
the central aperture in Iris. It regulates
and controls the amount of light
entering the eye.
Ciliary Muscles – They hold the lens in
position and help in modifying the
curvature of lens.
Retina – It is a delicate membrane
having enormous number of light
sensitive cells.
Optic Nerve – It transmits visual
information from retina to Brain.
Blind Spot – Thr point at which the
optic nerve leaves the eye.
Aqueous Humour – Between the cornea
and eye lens, there is a space filled with
transparent liquid, known as aqueous
humour which helps the refracted light
to be focused on retina. It also provides
nutrition to the eye.
Vitreous Humour – Space between eye
lens and retina is filled with a liquid,
known as Vitreous Humour.
Far Point of Eye:
Maximum distance to which eye can
see clearly, is called the far point of the
eye. For a normal eye, its value is
infinity.
Near Point of Eye:
Minimum distance at which an object
can be seen most distinctly without any
strain is called the least distance of
distinct vision. For a normal eye, it’s
value is 25cm.
POWER OF ACCOMODATION:
Case 1: To see far objects
Ciliary Muscles – Relaxed
Eye Lens – Thin
Focal length – Increase
Case 2: To see near objects
Ciliary Muscles – Contract
Eye lens – Thick
Focal Length – Decrease
MYOPIA (near sightedness)
A myopic person can see nearby objects
clearly but can’t see distant object
clearly.
Image is formed in front of retina.
Causes of Myopia:
Excessive curvature of eye lens
Stretching of eye ball.
Correction:
It is done by using concave lens of
appropriate power.
The concave lens placed in front of eye
forms a virtual image of distant object
at far point of the myopic eye.
The far point of a myopic eye is less
than infinity.
HYPERMETROPIA:
Affected person can see far objects
clearly but can’t see nearby objects
clearly.
The near point of eye moves away.
Image is formed behind retina.
Causes of Hypermetropia:
Focal length of eye lens becomes too
long.
Eyeball becomes too small.
Correction:
It is done by using convex lens of
appropriate power.
The near point of a hypermetropic eye
is more than 25cm.
The convex lens placed in front of a eye
forms a real image of near object on
retina.
Advantage of eyes in front of the face:
It gives a wider field of eye.
It provides three-dimensional view.
PRISM:
The splitting of white light into its
components due to different bending
ability for colours when it passes
through prism is called DISPERSION
OF LIGHT.
When light travels from denser medium
to rare medium with angle of incidence
greater than critical angle then the
refracted ray instead of emerging out
again goes into the same medium. This
is known as total internal reflection.
Two conditions:
Light travels from denser medium to
rarer medium.
The angle of incidence is greater than
critical angle.
Example: Optical Cables
Rainbow Formation:
c
