Refraction of light at a Plane Interface: Total Internal Reflection: Optical Fibre

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Refraction is the bending of a light ray from its path when it passes from one transparent medium to another at the interface of the two media.

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Refraction occurs because the speed of light changes from one medium to another. Greater the change in speed, greater is the bending of the ray.

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1) The incident ray, refracted ray, and the normal at the point of incidence lie in the same plane. 2) For a given pair of media and a given colour of light, sin i / sin r is constant.

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n1 sin i = n2 sin r, where n1 and n2 are the refractive indices of the first and second media, i is the angle of incidence, and r is the angle of refraction.

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Given: i = 30°, r = 20°. Formula: n = sin i / sin r. Step 1: sin 30° = 0.5. Step 2: sin 20° ≈ 0.342. Step 3: n = 0.5 / 0.342 ≈ 1.46. Answer: refractive index ≈ 1.46.

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When i = 0°, Snell's law gives r = 0°. So there is no bending of the ray at normal incidence.

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n = c / v. Here c is the velocity of light in vacuum and v is the velocity of light in the medium. It has no unit and is greater than 1 for a material medium.

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Given: n = 1.5, c = 3 × 10^8 m/s. Formula: n = c / v. Step 1: v = c / n. Step 2: v = (3 × 10^8 m/s) / 1.5 = 2 × 10^8 m/s. Answer: 2 × 10^8 m/s.