prepwalk

1. PHYSICS
REFRACTION OF LIGHT ON PLANE
SURFACES, CURVED SURFACES
AND GLASS PRISMS
Short revision series

2. Refractive index
 Refractive index = real depth
apparent depth
i
r
Medium 1
Medium 2

3. Laws of refraction
1. The incident ray, the reflected ray and the
normal at point of incidence all lie in the
same plane
2. SNELL’s law: The ratio of the sine of the
angle of incidence to the sine of the angle of
refraction is a constant for a given pair of
media
 the constant is known as the refractive
index
 ang = sin i (air) = velocity of light in air
 sin r (glass) velocity of light in glass

4. Eg
 If the angle of refraction is 200 , What is the
angle of incidence if the refractive index of
air to glass is 1.5?

5. solution
ang = sin i/sin r
1.5 = sin i/sin 20
sin i = 1.5sin20 = 1.36
i = sin-1 1.36

6. Refraction of light through a trangular
prism
 n = sin ½ (dm + A)
sin ½ A
 A= refracting angle of prism
 dm = minimum angle of deviation
i
r r
dm
A

7. Total internal reflection and critical
angle
 Total internal reflection occcurs when the
critical angle is exceeded for light travelling
from a dense to a less dense medium
 Critical angle is the incident angle at which
the angle of refraction is 900 when light
passses from a denser to a less dense
medium.
 ang = 1/sinC