IIT-JEE 2010 - Career Point

PHYSICS FUNDAMENTAL FOR IIT-JEE
Reflection at plane & curved surfaces
KEY CONCEPTS & PROBLEM SOLVING STRATEGY
Key Concepts :
(a) Due to reflection, none of frequency, wavelength
and speed of light change.
(b) Law of reflection :
Incident ray, reflected ray and normal on incident
point are coplanar.
The angle of incidence is equal to angle of
reflection
Incident n Reflected
Ray Ray
θ θ
Plane surface
Convex
surface
n
α α
n
Tangent
θ θ
at point P
P
Convex surface
A
Tangent
at point P
Some important points : In case of plane mirror
For real object, image is virtual.
For virtual object, image is real.
The converging point of incident beam behaves as a
object.
If incident beam on optical instrument (mirror, lens
etc) is converging in nature, object is virtual.
If incident beam on optical instrument is diverging in
nature, the object is real.
The converging point of reflected or refracted beam
from an optical instrument behaves as image.
If reflected beam or refracted beam from an optical
instrument is converging in nature, image is real.
P
Virtual
Object
P
Real
Object
P
Real
Object
n
n
P
Virual
Object
If reflected beam or refracted beam from an optical
instrument is diverging in nature, image is virtual.
For solving the problem, the reference frame is
chosen in which optical instrument (mirror, lens, etc.)
is in rest.
The formation of image and size of image is
independent of size of mirror.
Visual region and intensity of image depend on size
of mirror.
P
n
If the plane mirror is rotated through an angle θ, the
reflected ray and image is rotated through an angle 2θ
in the same sense.
If mirror is cut into a number of pieces, then the focal
length does not change.
The minimum height of mirror required to see the full
image of a man of height h is h/2.
Object
vsinθ
Object
Object
v
Rest
v
θ
vcosθ
v
v
θ
θ
α
α
Image
Rest
vsinθ
vcosθ Image
v m
2v m –v
Image
P'
P
n
Real
n
Object
α
α
α
α
P'
Virual
Object
Object
In rest
v m
Image
2v m
XtraEdge for IIT-JEE 26 DECEMBER 2009