REFRACTION OF LIGHT

Done by : SALAH A. AL SARY

Grade : Nine

Subject : Physics

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 to more dense mediumPasses from more dense to less dense medium

RefRaction of Light

What is RefLection 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.

What is Refraction of Light?

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

RefRaction Vs RefLection

Refraction Diagram

Incident ray : IORefracted Ray : ORNormal : NN’Surface of Separation

1. Incident angle ( i) :

angle between incident ray and normal2.Refracted Angle ( r ) :Angle between the refract ray and normal3.Angle of Deviation ( D ) : angle between the Prolongation of the incident ray and Refracted Ray

I

O

R

I’

‘

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

the medium ( speed of light vacuum ≈ speed of light in air).

Examples :

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 = 0 ᵒ

Deviated angle = 0 ᵒ

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

Example :

i= 60ᵒ

r= 40ᵒ

D = 60 -ᵒ 40 = ᵒ 20ᵒ

Air

water

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 .

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.

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

Cases of refraction :when light passes from water to Air :

Case 2 : i = 48.6ᵒ , il = 48.6 ᵒ ( i = il )

The ray grazes the surface of separation .

r = 90ᵒD = r – i D = 90 - 48.6 = 41.4ᵒ ᵒ ᵒ

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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