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


What is angle of incidence, angle of refraction, angle of emergence and angle of deviation in this case?

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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Davneet Singh
Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 9 years. He provides courses for Maths and Science at Teachoo.