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1. Refraction of Light
LIGHT

2. LIGHT
Refraction is the change in
direction of light when it passes
from one medium to another.

3. LIGHT
If light ray enters another medium perpendicular to
boundary, the ray does not bend.

4. LIGHT
When the light ray travels
from air to water, the
refracted ray bends
towards the normal.
i
r
air
water
Incident ray
Refracted ray
normal
i – angle of incidence
r– angle of refraction

5. LIGHT
When the light ray travels
from water to air, the
refracted ray bends away
from the normal.
i
r
air
water
Incident ray
Refracted ray
normal
i – angle of incidence
r– angle of refraction

6. LIGHT
During refraction, light
bends first on passing
from air to glass and
again on passing from
the glass to the air.

7. LIGHT
During refraction, light
bends first on passing
from air to glass and
again on passing from
the glass to the air.
i
r
Incident ray
Emergent ray
Refracted ray
Reflected ray
air
air
glass

8. LIGHT
Light slows down when it enters an optically denser
medium. The refracted ray bends towards the normal
when the second medium is optically more dense than
the first.
i
r
air
water
Incident ray
Refracted ray
normal

9. LIGHT
Light speeds up when it enters an optically less dense
medium. The refracted ray bends away from the normal
when the second medium is optically less dense than
the first.
air
water i
r
Incident ray
Refracted ray
normal

10. LIGHT
Among the 3 transparent mediums (air, water and
glass), glass has the highest optical density.
air
water
i1
r1
Incident ray
Refracted ray
glass
i2
r2
Refracted ray
air
water
i1
r1
Incident ray
glass
i2
r2
Refracted ray
Refracted ray

11. LIGHT
Complete these ray diagrams.
air
glass glass
water

12. LIGHT
Complete these ray diagrams.
airwater
glassair

13. LIGHT
The incident ray, the refracted ray and the normal
at the point of incidence all lie in the same plane.

14. For two given media, the ratio
sin i ÷ sin r is a constant,
where i is the angle of
incidence and r is the angle
of refraction
LIGHT
i
r
air
water
Incident ray
Refracted ray
normal
Refractive
Index, n =
sin i
sin r

15. LIGHT
The higher the optical density, the greater the
refractive index. The greater the refractive index, the
greater the bending of light towards the normal.
air
water
i1
r1
Incident ray
Refracted ray
glass
i2
r2
Refracted ray
air
water
i1
r1
Incident ray
glass
i2
r2
Refracted ray
Refracted ray

16. LIGHT
If light is incident upon a piece of glass (refractive
index 1.52) at an angle of 45o
, what is the angle of
refraction?

17. LIGHT
Given that the refractive index of water is 1.33,
calculate the angle of refraction when the incident
ray comes in at 60o
to the normal.
60o
r
air
water
Solution
n =
sin i
sin r
1.33 =
sin 60o
sin r
sin r
=
sin 60o
1.33
r = 40.6o

18. LIGHT
When light travels from a
less dense medium to a
denser medium…
n =
sin i
sin r
i
r
air
water
When light travels from a
denser medium to a less
dense medium…
n =
sin r
sin i
i
r
air
water

19. LIGHT
The figure shows light travelling from water into the air. The
ray is incident upon the boundary at 30o
. What is the angle of
refraction if the refractive index of water is 1.33?
30o
r
air
water
Solution
n
sin r
sin i
=
1.33
sin
30o
sin r
=
sin r= 1.33sin
30o
r
=
41.9o

20. LIGHT
Other ways of calculating the refractive index…
Refractive
index, n =
Speed of light in
vacuum / air
Speed of light in
medium
=
c
v

21. LIGHT
Take a look at this...

22. LIGHT
The critical angle is the angle of incidence in the
optically denser medium for which the angle of
refraction is 90o
.
When i = critical angle,c
r = 90o
.

23. LIGHT
This is called TOTAL INTERNAL REFLECTION.
When i > critical angle, the ray gets reflected internally.

24. LIGHT
For TOTAL INTERNAL REFLECTION to take place:
The light ray must travel from an optically denser
medium towards a less dense one.
The angle of incidence must be
greater than the critical angle.
Direction of light path
i

25. LIGHT
How do we calculate the critical angle?
We know that r = 90o
…

26. LIGHT
We know that when
light travels from a less
dense medium to a
denser medium
Refractive
Index, n =
sin r
sin i
We know that when
light travels from a
denser medium to a
less dense medium
Refractive
Index, n =
sin r
sin i

27. LIGHT
How do we calculate the critical angle?
We know that r = 90o
…
Refractive
Index, n =
sin r
sin i
n =
sin c
sin 90o
=
sin c
1

28. LIGHT
How do we calculate the critical angle?
n
=sin c
=c
1
sin-1
n
1

29. LIGHT
Medium:
Refractive
Index:
Critical Angle:
=c sin-1
n
1
Glass
1.50
= sin-1
1.50
1
= 41.8o

30. LIGHT
Medium:
Refractive
Index:
Critical Angle:
=c sin-1
n
1
Water
1.33
= sin-1
1.33
1
= 48.8o

31. LIGHT
Medium:
Refractive
Index:
Critical Angle:
=c sin-1
n
1
Diamond
2.42
= sin-1
2.42
1
= 24.4o

32. LIGHT
Total Internal Reflection in Prisms

33. LIGHT
Total Internal Reflection in Prisms

34. LIGHT
Fibre Optics