Transcript refrac_reflect

LIGHT
REFRACTION
TOTAL INTERNAL
REFLECTION
OPTICAL FIBRES
BY : A . Ananda
Military School Bangalore
 Bending of light when it travels from one
optical medium to another is called refraction.
 The ray of light bends towards the normal
when it travels from rarer to denser medium.
 The ray of light bends away from the normal
when travels from denser to rarer medium.
 The ray of light is refracted because the
speed of light is different in different media.
ILLUSTRATIONS:
 A coin placed under water appears raised.
 A stick immersed in water partially, appears
bent.
Laws of refraction:
 The incident ray, the reflected ray and the
normal drawn at the point of incidence all lie in
the same plane
 For a given pair of media and given color the
ratio of the sine of the angle of incidence to the
sine of the angle of refraction is a constant
# This is called Snell’s law
# The ratio is called the refractive index of the
medium represented by µ = sin i/sin r
 Refractive index is also given by:
Velocity of light in air or vacuum
Velocity of light in medium
v
 = c
MEDIUM
REFRACTIVE INDEX
water
Glass
Diamond
1.33
1.5
2.42
© Refracted ray bends away from the normal
when it travels from denser to rarer medium.
© As the angle of incidence is increased, angle
of refraction also increases.
© For a particular angle of incidence in the
denser medium called critical angle, the angle of
refraction in the rarer medium is 90o
90o
air
C
water
Object
© For any angle of incidence greater than
critical angle, the ray of light turns back to the
same medium.
© This is called total internal reflection.
 For critical angle; since light is traveling from
denser medium to rarer medium:1

=
sin i
sin r
OR
= sin c = sin C
sin 90o
1
 = 1/sin C
CONDITIONS FOR TOTAL
INTERNAL REFLECTION:
 The ray of light should travel from denser to rarer
medium.
 Angle of incidence should be greater than critical
angle for a given pair of media.
 Ex : Critical angle with air for different mediaWater = 48o Glass = 42o diamond = 24o
ILLUSTRATIONS:
 Mirage – an optical illusion that appears in deserts
during summer
 Looming : The image of ship appears hanging in air
due to mist and fog for a person on the shore.
 Sparkling of diamond.
APPLICATIONS:
 Total reflecting prisms:
i) To turn a ray through 90o
Used in periscope
90o
ii) To turn a ray through 180o
90o
iii) Erecting prism:
Used in prism binoculars
90o

OPTICAL FIBRES:
USES:
 In medicine – Endoscopes
 Optical sensors – used computers and detectors
 Telecommunication.
 Laser probes , etc.,
Sources:
© Science encyclopedia – CD ROM
D K Multimedia
1. Mirage. 2. Looming. 3. Optical fiber
© NCERT Text.
Presented by:
A Ananda
Military School
Bangalore