Question

State the laws of refraction of light. If the speed of light in vacuum is 3X108 ms-1, find the speed of light in a medium of absolute refractive index 1.5.

Answer 1

1st part -

There are two laws of refraction of light.

(a) The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant. This in known as Snell's law. Mathematically, it can be expressed as - Sin i/sin r = n₁₂

Here, n₁₂ is the relative refractive index of medium 1 with respect of medium 2.

(b) The incident ray, the refractive ray and the normal to the interface of two media at the point of incidence lie on the same path.

2nd Part -

Speed of light in vacuum = 3 × 10⁸ m/s

Refractive index of the medium = Speed of light in vacuum/Speed of light in medium

⇒ 1.5 = 3 × 10⁸/v

⇒ v = 2 × 10⁸ m/s

Hence, the speed of light in the medium of refractive index 1.5 is 2 × 10⁸ m/s.

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