Chapter-9|Ray Optics and Optical Instrument|NCERT 12th Physics:


A Prism is a portion of a transparent medium bounded by two plane faces inclined to each other at suitable angle.

Refraction of Light Through a Prism:

Lat us consider a triangular prism ABC.

Let angle of incidence and angle of refraction at first phase AB are i and r₁

The angle of incidence at the second face AC is r₂ and the angle of emergence is e.

The angle between emergence Ray RS and incident ray PQ is called angle of deviation δ.

If μ is the refractive index of material of the prism, Then according to Snell’s law-

This is the angle through which a ray deviates on passing through the thin prism of small refracting angle A.

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