Principle of Reversibility of Rays

• In the first figure → ray passes from A to material and to B.
• In second figure → light source is moved to B and a ray is sent in the opposite direction. → it is found that ray will reach A via the exact same path in the first figure. → there is no change in angles x and y. This is called the principle of reversibility of light.

Law

Principle of Reversibility of Light rays → states that regardless of how many times a light ray has been reflected or refracted → it will follow the same path when its direction is reversed

→ due to the principle of reversibility of rays → refractive index of the material is always given by $n=\frac{sinx}{siny}$ regardless of whether goes from A to B or B to A

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