This document discusses the refraction of light, including that light bends when moving between media of different densities, following Snell's law. It also covers total internal reflection, where light reflects totally inside a denser medium if the angle of incidence exceeds the critical angle.

1. Chapter 5
Refraction of Light at Plane Surfaces
Summary:
Refraction of light: The process of changing speed at an interface when light
travels from one medium to another resulting in a change in direction in
another medium is “refraction of light”.
• In refraction, bending of light takes place.
• No bending when light incidents normally.
• Refractive index is a property of transparent medium.
• Refractive index is a dimensionless quantity.
• Absolute refractive index = Speed of light in vacuum(c)/Speed of light in
Medium(v)
n = c/v
• If refractive index is high, speed of light is low.
• Refractive index depends on 1) nature of material, 2) wavelength of
light
• Relative Refractive index = Speed of light in medium 1/ speed of light
in medium 2
=
Refractive index of second medium
Refractive index of first medium
n 21 =
𝑛2
𝑛1
• When light travels from rarer (air) to denser medium (glass),
✓ Light bends towards the normal in denser medium.
✓ Angle of refraction(r) is less then angle of incidence (i)

2. Snell’s law:
sin i
sin r
=
𝒗 𝟏
𝒗 𝟐
=
𝑛2
𝑛1
Or
n1 sin i = n 2 sin r (or) sin i/ sin r = constant
This is called Snell’s law.
Laws of refraction:
1) The incident ray, the refracted ray and the normal to the interface of
two transparent media, at the point of incidence, all lie on the same
plane.
2) Light follows Snell’s law in refraction.
Critical angle: When light travels from denser medium to rarer medium,
1) The angle of incidence is called critical angle(C) if the angle of
refraction is 900
Total internal reflection: If the angle of incidence is greater than the
critical angle when the light ray passes from denser medium to rarer medium,
then the light ray totally internally reflected back into the denser medium. This
is called “total internal reflection”.
Multiple Choice questions:
1. For critical angle, the angle of refraction is ___________ [ ]
a) 900
b) 450
c) 600
d) 1800
2. Which of the following is Snell’s law
a) n 1 sin i = sin r/ n 2 b) n 1/ n2 = sin r/sin i
b) n2/ n1 = sin r/ sin i d) n2 sin i = constant
3. The refractive index of glass with respect to air is 2. The critical angle of
glass air interface is______________ [ ]

3. a) 00
b) 450
c) 300
d)600
4. Total internal reflection takes place when the light ray travels from ___
[ ]
a) Denser to rarer medium b) Denser to denser medium
a) Rarer to denser medium d) rarer to rarer medium
5.The angle of deviation produced by glass slab is [ ]
a) 00
b) 200
c) 900
d) Depends on the light ray and normal to
slab.
6.Mirage is an example of _______________ [ ]
a) Total internal reflection b) Refraction c) Reflection
d)None of the above.
7. Refractive index of glass relative to water is 9/8. What is the refractive index
of water relative to glass? [ ]
a) 9/8 b) 8/9 c)1/9 d) None
8. Optical fibre works on [ ]
a) Reflection b) Refraction c) Total internal reflection d) All of these
KEY
1. a 2. b 3. c 4.a
5.a 6.a 7. b 8.c