This document summarizes key concepts about light refraction including: - Refraction occurs when light travels from one medium to another with different optical densities, causing the light's speed and direction to change. - The refractive index quantifies how much a medium slows light down relative to a vacuum. It is defined as the ratio of the speed of light in a vacuum to the speed of light in the medium. - Snell's law mathematically relates the angles of incidence and refraction to the refractive indices of the two media and is useful for calculating refraction. - Refraction can make objects appear in different locations than their true positions, such as making deep pools appear more shallow.

1. LIGHT AND OPTICS

2. CONTENT IN THIS CHAPTER

3. 6.1 REFRACTION OF LIGHT
• SC1: 6.1.1 DESCRIBE REFRACTION OF LIGHT
• SC2: 6.1.2 EXPLAIN REFRACTIVE INDEX, N.
• SC3: 6.1.3 CONCEPTUALIZE SNELL'S LAW
• SC4: 6.1.5 EXPLAIN REAL DEPTH AND APPARENT DEPTH.
• SC5: 6.1.7 SOLVE AT LEAST ONE PROBLEM RELATED TO
REFRACTION OF LIGHT.

4. Refraction of light is the change in velocity of
light when travelling through mediums of
different optical densities
i
r
air
glass
Incident ray
Refracted ray
i
r
Emergent ray
Ray of light travel from air (less
dense) to glass (denser)
 i > r
 The speed of light decreases.
The ray of light bend towards
the normal
Ray of light travel from glass
(denser) to air (less dense).
 i < r
 The speed of light increases.
The ray of light bend away from
the normal

5. OPTICAL DENSITY VS PHYSICAL DENSITY
 Both are different parameters
 A material with greater optical density
than water does not imply it has a
greater physical density than water
 For example paraffin oil is optically
denser than water but less dense than
water
Medium Refractive
index, n
Paraffin oil 1.44
Water 1.33
REFRACTIVE INDEX, n
 Refractive index, n is the ratio of speed
of light in vacuum to the speed of light
in medium.
 n =
Speed of light in vacuum
Speed of light in medium
=
c
v
Where speed of light, c = 3.0 x 108
ms-1
 No unit because it is ratio between two
speeds
Medium Refractive
index
Vacuum and
air
1.00
Olive oil 1.46
Perspex 1.50
Crown glass 1.52

6. The speed of light in benzene is 2.0 x 108 ms-1. If the speed of
light in vacuum is 3.0 x 108 ms-1, calculate the refractive index
of benzene.
Exercise
n = 1.5

7. Snell’s law
Law of Refraction
There are two laws of refraction:
1) The incident ray, the refracted ray and normal meet at one point and are in
the same plane
2) The value of
sin 𝑖
sin 𝑟
is a constant, where i is the angle of incident while r is the
angle of refraction. (Also known as Snell’s law)
n1 sin θ1 = n2 sin θ2
When medium 1 is air ( n=1) and medium 2, n2 = n
n =
sin 𝑖
sin 𝑟 n =
sin 𝑖
sin 𝑟
Derivation:
https://youtu.be/4ccXzZt4ID8

8. 1. The figure below shows a light ray passing through a
plastic block.
The refractive index of the plastic block is 1.24. If the
speed of light in vacuum is 3.0 x 108 ms-1 , find
a) the speed of light in the plastic block
b) the angle of refraction, r
v = 2.42 x 108 ms-1
R = 34.8
2. The figures below show a ray of light travelling
from air to glass at different angles of incidence.
Calculate the refractive index of the glass.
n = 1.46
n = 1.22

9. A light ray travels from
optically less dense medium
to an optically denser
medium.
Since θ1 > θ2 ,
i = θ1 r = θ2
Hence,
n =
sin 𝑖
sin 𝑟
=
sin 𝜃1
sin 𝜃
A light ray travels from
optically denser medium to an
optically less dense medium.
Since θ2 > θ1 ,
i = θ2 r = θ1
Hence,
n =
sin 𝑖
sin 𝑟
=
sin 𝜃2
sin 𝜃1
Reversibility of light

10. Real depth AND Apparent depth
Refraction of light gives us false impression of depth.
Example of situation:
1) Water in a deep pool appears than it really is.
2) The image of the fish appear closer to the water surface
n =
𝑟𝑒𝑎𝑙 𝑑𝑒𝑝𝑡ℎ,𝐻
𝑎𝑝𝑝𝑎𝑟𝑒𝑛𝑡 𝑑𝑒𝑝𝑎𝑡ℎ,ℎ

11. Phenomenon due to refraction of light
Setting of the Sun Twinkling of stars

12. Exercise
1. Apparent depth of a coin in a glass
of with water is 3.2 cm. If the refractive
index of water is 1.33, calculate the
actual depth of the coin.
2. In the figure below, a coin is placed
at the bottom of a glass container of
height 40 cm. The image of the coin is
seen by an observer from the top of
the container.
If the refractive index of the glass
block is 1.5, what is the height of x?