CBSE Class 10 Answered

The critical angle is the angle of incidence above which total internal reflection occurs.

Total internal reflection is an optical phenomenon that occurs when a ray of light strikes a medium boundary at an angle larger than a particular critical angle with respect to the normal to the surface, and gets completely reflected into the same medium than refracted into another medium.

Refractive Index = Speed of light in Reference medium/Speed of light in given medium.

So when we specify the Reference medium, the symbol n should explicitly show it.

²n₁ = Refractive index of second medium with respect to first = Spee of light in first medium/Speed of light in second medium.

When the reference medium is vacuum, we just denote,

n₂ or n₁

Now it's easy to see that n²₁ or ²n₁ = n₂/n₁ = (c/v₂)/(c/v₁) = v₁/v₂

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