grade 9 physics

1. REFRACTION OF LIGHT
Done by : SALAH A. AL SARY
Grade : Nine
Subject : Physics

2. Contents :
1.Definition
2.Difference between RefRaction and
refLection of Light
3.Labeling Refraction Diagram
4.Index of refraction
5.Path of Light when it:
Falls perpendicularly on the surface of
separation
Passes from less index to more medium
Passes from more denser to less denser
medium

3. RefRaction of Light

4. What is RefLaction of Light?
 Reflection is when light bounces off an object. If
the surface is smooth and shiny, like glass, water
or polished metal, the light will reflect at the
same angle as it hit the surface.

5. What is Refraction of Light?
 Refraction is when the speed and direction
of light changes, as light moves from one
transparent medium to another.

6. RefRaction Vs RefLection

7. Refraction Diagram
Incident ray : IO
Refracted Ray : OR
Normal : NN’
Surface of Separation
1. Incident angle ( i) :
angle between incident ray and normal
2.Refracted Angle ( r ) :
Angle between the refract ray and normal
3.Angle of Deviation ( D ) :
angle between the Prolongation of the incident ray and Refracted Ray
I
O
R
I’
‘

8. Index of refraction of a
medium
 Ratio of the speed of light in vacuum to the speed of light in
the medium.

9. Examples :

11. When Light Falls Perpendicularly
on the surface of separation :
 When a ray of light is incident perpendicularly on
the interface between two transparent media, it enters the
new medium without Deviation .
 Incident angle = 0ᵒ
 Refracted angle = 0ᵒ
 Deviated angle = 0ᵒ

12. Passage of light from less to
more dense medium :
When the light is passing from air (less dense)
into water (more dense), it is bent towards the
normal.
i > r
D = i – r

13. Example :
 i= 60ᵒ
r= 40ᵒ
D = 60 -ᵒ 40 =ᵒ 20ᵒ
Air
water

14. Passage of light from more to
less dense medium :
 When light passes from a more dense to a less dense
substance, (for example passing from water into air),
the light is refracted (or bent) away from the normal.
In this case we must take in consideration the
LIMITING ANGLE il .

15. Limiting angle il ( Critical angle)
The smallest angle of incidence at which a light ray
passing from one medium to another less refractive
medium can be totally reflected from the boundary
between the two.
 For the water-air boundary, the critical angle is 48.6-degrees.
 For the crown glass-water boundary, the critical angle is
61.0-degrees.

16. Cases of refraction :when light
passes from water to Air :
For the water-air boundary, the critical angle is 48.6-
degrees
Case 1 : i = 40ᵒ , il = 48.6ᵒ ( i < il )
The light is refracted (or bent) away from the normal.
D = r – i
D = 60ᵒ – 40ᵒ = 20ᵒ

17. Cases of refraction :when light
passes from water to Air :
Case 2 : i = 48.6ᵒ , il = 48.6 ᵒ ( i = il )
The light is refracted grazes the surface of
separation .
r = 90ᵒ
D = r – i
D = 90 - 48.6 = 41.4ᵒ ᵒ ᵒ

18. Cases of refraction :when light
passes from water to Air :
Case 3 : i = 60ᵒ , il = 48.6 ᵒ ( i = il )
The light undergoes TOTAL INTERNAL
REFLECTION .
i= r = 60ᵒ

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