Concepts

Class 10
Chapter 11 Class 10 - Human Eye and Colourful World

When we a say a glass prism, we mean a triangular glass prism

## What is a Triangular Glass Prism?

It is a glass object made up of

• 3 Rectangular sides
• 2 Triangular ends

Here, refraction occurs on the two sides of equilateral triangle

We can see that the two faces are not parallel to each other

In a rectangular glass slab (link), the two faces are parallel but in a prism... they are not parallel

## What is Refraction of Light in case of Glass Prism

When light ray falls on one side of prism, it gets refracted (bent towards the normal)

It is because it has moved from an optically rarer medium (air) towards optically denser medium (prism)

When these ray reach the other side of prism, it gets refracted again (bent away from normal)

It is because now it has moved from an optically denser medium (prism) towards optically rarer medium (air)

In the figure,

• ∠i – Angle of incidence
• ∠r – Angle of refraction
• ∠e – Angle of emergence
• ∠A – Angle of the prism
• ∠D – Angle of deviation

## What are Incident Ray, Refracted Ray and Emergent Ray in Case of Prism

The Light Ray which falls on prism is called Incident ray

The light Ray which is refracted (bent on enterting prism) is called Refracted Ray

Light ray which emrges out of Prism is called Emergent RAY

## Angle of Incidence

The angle between incidence ray and normal ray is called Angle of Incidence

### Angle of Refraction

The angle between refracted ray and normal ray is called Angle of Refraction

### Angle of Emergence

The angle between emrgent ray and Normal at other side of prism is the angle of emergence

### Angle of Deviation

If Incident ray is extended forwards and Emergent ray is extended backwards

They tend to meet at point O

Angle made by emergent ray with the incident ray at this point is called Angle of Deviation

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