When light travelling in one medium falls on the surface of second medium the following three effect may occur. 1:- A part of incident light is reflected back into the same medium. This is called Reflection of light. 2:- A part of light is passes through the medium.This Is known as Refraction of light. 3:- And remaining part of the light is absorbed by the surface on which the light fall. This is known as Absorption of light.

2. Nature of light.
Introduction.
Basic law of refraction.
Snell’s law of refraction.
Refraction through Glass slab.
Causes of refraction.
Refraction through glass prism.
Terminology.
Angle of deviation Vs angle of incidence.
Refraction by curved surface.
Refraction by spherical lenses.

3. Refraction by spherical lenses.
Refraction by convex lens.
Refraction by concave lens.
Refraction by cylindrical lens.
Spherical lens versus cylindrical lens.
Refraction and the Eyes.
Refraction for distance and near vision.
Refraction caused by eye lens.

4.  Rectilinear propagations of light.
 When light travelling in one medium falls on
the surface of second medium the following
three effect may occur.
1:- A part of incident light is reflected back
into the same medium. This is called
Reflection of light.
2:- A part of light is passes through the
medium.This Is known as Refraction of light.
3:- And remaining part of the light is absorbed
by the surface on which the light fall. This is
known as Absorption of light.

5.  Definition-The phenomenon of the bending of
light as it passes obliquely from one transparent
medium to another due to change in density of
medium and speed of light.
 The path along which the travel in the first
medium is called INCEDENT RAY .
 And that in the second medium is called
REFRACTED RAY.
 The angle which the incident ray and the
refracted ray makes with the normal at the
surface of separation are called “angle of
incidence” and “angle of refraction”

7. First law:- The incident ray,
Refracted ray and the normal to
the surface at the point of
incidence all lie in the same
plane.
Second law:- The ratio of the
angle of incidence to that of the
angle of refraction is constant
for a given pair of media
This law is also known as snell’s
law of refraction.

8.  Discovered by Willobrord Snellius in1621.
 It is used to describe the relation between
angle “i” and angle “r” when light passing
through a boundary b/w two different
isotropic media such as Glass or Air.
 In experimental optics it is used to find the
refractive index of material.
 RELATION :-

9.  Whenever a refraction occur through glass
slab three phenomenon will be occur
1:- When a ray passes from optically rarer to
denser medium it bends towards the normal
i.e angle “i” greater than angle “r” .
2:-When a ray passes from optically denser to
rarer medium it bends away from the normal
i.e angle “r” greater than angle “i” .
3:- A ray of light travelling along the normal
passes undeflected i.e- angle “i” is equal to
angle “r”

11. 1:-When parallel light ray
fall obliquely upon a glass
plate(with parallel side)
there direction is
changed on account of
the retardation of one
edge of the beam before
the other.
2:-When entire width of
beam has entered the
substance of the glass, all
the ray will be equal
retarded throughout ,and
consequently travelling at
a uniform through
lessened speed .

12.  The amount by which the beam of light is bent
depend on three factors these are as follows,
 1:- Optical density- The bending of light is
dependent on the retardation of light the more
resistance the body offers the more slowly will be
light be made to travel.
 2:- Refractive index- It is the relation b/w angle of
incidence and angle of refraction.Because of this
relation the more oblique the light ray the greater
will be the bending.
 3:- Wavelength- Blue light is more bent than red
light because of difference in wavelength.

13.  A prism is a transparent optical element with flat,
polished surface that refract light.
 When a light ray fall on a non parallel surface
(PRISM) the direction of light also change. The
incident beam of light is retarded and bent round
and run through the substance of the glass until
reaches the another surface . Consequently the
beam is bent round further in the same sense and
is deviated out of its original path altogether .
 since a ray on entering the denser medium
(GLASS) from a rare one (AIR) , the incident ray
bends towards the base as it enter the PRISM .

14.  Light after passing through a prism travels on in
a parallel beam ,it is never brought to a Focus
and no image is formed .
 But in the prism the light source should be
shifted to apex when seen from the base of
another side.

15. 1:-Angle of incidence- The angle b/w the incidence ray and
the normal.
2:- Angle of refraction- The angle b/w the refracted ray
and the normal.
3:- Angle of deviation- The angle b/w the incidence ray and
the emergent ray.
4:-Angle of minimum deviation- The minimum value of the
angle of deviation suffered by a ray on passing through a
prism .
The main phenomenon of the prism is to deviate the white
light into seven colors which can be appear as spectrum
on screen.

17. The given fig shows the variation of angle of
deviation with the angle of incidence “i”.
For a given prism and for a given pair of light ,
the angle of deviation depends upon the angle i
only i.e.-
.

20.  Refraction in spherical lenses occur because in these
lenses all the meridian have same curvature , so the ray
coming from infinity should be focus at a point.
 When the parallel light is passes through the lens ,the
light ray is converge or diverge because of prismatic effect
in lenses. As shown in given figures:-

21. When light ray go through a
CONVEX IENS the light ray are
refracted and show convergence
and all the ray meet at a point
on a principal axis known as
FOCUS and form real and
inverted image.
For any ray entering the lens that
is not along a normal the light
will change direction because
here change in media occurs i.e.
light ray travel from Rarer-
Denser-Rarer.
A ray entering along the normal
passes straight without any
deviation because lens can also
act as parallel plate glass slab.

22. The basic difference b/w the
refraction of convex and concave
is the nature of lens.i.e convex
les is of converging nature
whereas concave lens is of
diverging nature so all the
parallel beam of light passes
through the concave lens are
diverging so these rays never
meet at focus actually but appear
to meet at focus and form virtual
and erect image of object.
In this phenomenon refraction
also occurs due to change in
media i.e. Rarer-denser-rarer.

23. 1:-A cylindrical lens is a piece
of glass , one of the surface of
which is cylindrical.
2:-A cylindrical lens is a lens
which focuses light into a line
instead of a point .
3:-This lens compresses the
image in the direction
perpendicular to the image
line.
4:- A Cylindrical lens has two
meridians.i.e
one is plane meridian having
no power and plane
perpendicular to plane
meridian is known as power
meridian.
5:- This lens is used to correct
astigmatism.

24. SPHERICAL LENS
1:- Spherical lens are used
to correct
distance.(Myopia and
hypermetropia).
2:-Spherical lens have same
power in all meridian .
3:- it can focus the light into
the point image .
4:-Spherical lens is curved
both vertically and
horizontally.
5:-Spherical lens is the best
for distortion free vision
due to its shape.
CYLINDRICAL LENS
1:- this lens is used to correct
astigmatism.
2:-This lens have different
power in different
meridians.
3:-This lens cannot form the
point image but focus the
light as line parallel to
cylindrical axis.
4:- This lens is flat vertically
and curved horizontally
across face.
5:-Cylindrical lens are flat at
the edge , which can cause
distortion at certain angles.

25. 1:- Refraction is the phenomenon
which makes the image
formation possible by eyes.
2:-Most of the refraction in the
eyes takes place at first
anterior most surface of the
eye i.e. CORNEA.
3:- Since the refraction through
cornea takes place because
large change in the Refractive
index which the light
experiences.
4:- About 80% of the refraction
occur through cornea while
rest of 20% refraction occur
through crystalline lens.
5:- The image formed at retina is
inverted but our brain convert

26. In distance vision light rays from distance object
are parallel ,so no much refraction occurs in
this case
In close vision light rays that are coming from closer
object are diverges and need much refraction to focus
properly.

27. In our eyes there are total six elements through
refraction occurs these are:-
anterior surface of cornea, the substance of cornea,
the posterior surface of cornea, the aqueous
humour, the anterior surface of lens, the posterior
surface of lens, the substance of lens and vitreous
humour.
But the refraction at the posterior surface of cornea is
ignored because the R.I. is same as that of aqueous
humour.
The light entering the eyes is refracted at the anterior
surface of cornea because of the two reason-
1:- curvature of cornea.
2:- Difference in R.I. of air and cornea.

28. 1:-Since lens is made of several
layer so central nucleus have higher
R.I. than the cortical layer.
2:- The curvature of the outer layer
of lens is less than that of the inner
,so the central nucleus is more
spherical than the cortical layer. so
refraction is greater at the
central region of the lens than
the cortical region.
3:-The comparatively greater
refractive strength of the central
region of lens has a biological
significance.
A:- It reduces the amount of
scattered light within the eyeball.
B:- It reduces the spherical and
chromatic aberration.