OPTICS
Ray
optics
Rectilinear
propagation
Laws of reflection
and refraction
Wave
optics
Interference,
diffraction
polarisation
OPTICAL PHENOMENON
a) Reflection
b) Refraction
c)Absorption
A) Reflection
bouncing back of light
LAWS OF REFLECTION
 Angle of incidence is equal to the angle of reflection
i = r
 The incident ray, the reflected ray and the normal all
lie in the same plane.
IMAGE
It is a point where atleast two light rays actually meet or
appear to meet.
 Real image
 Virtual image
Real image
 light rays actually meet after
reflection.
 Can be obtained on screen.
 Inverted.
 Eg., image formed on cinema
screen.
Virtual image
 light rays diverge after
reflection.
 Can’t be obtained on screen.
 Erect
 Eg., image formed by plane
mirror or convex mirror
Spherical Mirrors
A spherical mirror has the shape of a section of
a sphere. If the outside is mirrored, it is convex;
if the inside is mirrored, it is concave.
SPHERICAL MIRRORS
RELATION BETWEEN FOCAL LENGTH
AND RADIUS OF CURVATURE
R = 2f
f=R/2
CONCAVE MIRROR
f=R/2
CONVEX MIRROR
f=R/2
MIRROR FORMULA FOR CONCAVE MIRROR
OO’C and II’C are similar triangles
OO’ =
II’
CO
IC
II’F and NAF are similar triangles
NA = NF
II’ FI
OO’ = NF
II’
FI
CO = PF
IC FI
(But NA = OO’)
(NF = PF)
PO-PC = PF
PC-PI
PI-PF
-u + R = -f
-R + v -v + f
1+1=1
v u f
( since R = 2f )
-u + 2f = -f
-2f = v -v + f
Valid cases : 1. Object based on principal axis
2. Small aperture
3. In paraxial rays
MIRROR FORMULA FOR CONVEX MIRROR
OO’C and II’C are similar triangles
OO’ =
II’
CO
IC
II’F and NAF are similar triangles
NA = NF
II’ IF
OC = PF
IC IF
OO’ = NF
II’
IF
But NA = OO’
NF = PF
PO+PC = PF
PC-PI
PF-PI
-u + R = f
R-v
f-v
since R = 2f
1+1=1
v u f
-u + 2f = f
2f - v
f-v
Mirror Equation Sample Problem
•C
•F
Suppose AllStar, who is 3 and
a half feet tall, stands 27 feet
in front of a concave mirror
with a radius of curvature of
20 feet. Where will his image
be reflected and what will its
size be?
di = -15.88 feet
hi = -2.06 feet
MIRROR EQUATION SAMPLE PROBLEM 2
•F
•C
Casey decides to join in
the fun and she finds a
convex mirror to stand
in front of. She sees her
image reflected 7 feet
behind the mirror which
has a focal length of 11
feet. Her image is 1
foot tall. Where is she
standing and how tall is
she? d =-19.25 feet
o
ho = 2.75 feet
LINEAR MAGNIFICATION BY SPHERICAL MIRRORS
The linear magnification produced
by a spherical mirror is the ratio
of the size of the image formed
by the mirror to the size of the
Object, both measured perpendicular
to the principal axis.
m = hi
ho
∠O’PO = ∠OPD
(I=r)
∠O’PO = ∠OPI’ ( I=r) and ∠O’OP = ∠I’IP = 90°
OO’P and II’P are similar triangles
II’ = PI
OO’
PO
Since II’ = -hi ; OO’ = ho ; PI = - v ; PO = - u
- hi = - v
or
hi = - v
ho
u
ho
u
m=-v
u
1+1=1
v u f
OTHER FORMULA FOR MAGNIFICATION
m=f–v
f
m= f
f-u
Virtual, erect
Real, inverted