Page 173 - Physics_Form_2

Refraction and dispersion of light

various experimental observations, two
laws govern the behaviour of a light ray
as it strikes the interface between two
media of different optical densities. These
laws are known as the laws of refraction
Glass block
of light.
FOR ONLINE READING ONLY

Activity 5.4

Aim: To deduce the laws of
refraction and determine
the refractive index
Figure 5.5
Materials: A rectangular glass block,
Question four optical pins, a white
Describe the path taken by a light ray sheet of paper, a piece
travelling from the air into the glass of soft board, a pencil, a
block and the air again. protractor, paper pins, a
computer or tablet with
spreadsheet software
The lines PP , MN and P P show the
34
12
path that a light ray follows from air, Procedure
through the glass block and to air again. 1. Place the glass block on the sheet
Light rays are refracted as they pass from of paper and trace its outline using
air to glass (at the first boundary) and a pencil.
again as they pass from glass to air (at the
second boundary). 2. Remove the block.
3. At point E (near the centre of the
longer edge of the outline), draw a
Laws of refraction normal to the outline as shown in
When a beam of light passes through two Figure 5.6.
different media via an interface, it bends.
The amount of bending depends on the
optical densities of the two media and
the angle of incidence of the light beam.
Note that, the angle of incidence and the
angle of refraction differ in proportion to
the difference in the optical densities of
the two media. If a light ray passes from
the optically less dense medium to the
optically denser medium, it is bent towards
the normal. However, if the ray travels
from a medium of higher optical density
to a medium of lower optical density, it
bends away from the normal. Following Figure 5.6

167

Physics Form 2 Final.indd 167 25/10/2025 10:27