Which one of the following statements is correct regarding the travel

Which one of the following statements is correct regarding the travel of a light beam from a rare to a dense medium?

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A light beam travelling from a rare medium to a dense medium slows down and bends towards the normal.

A light beam travelling from a rare medium to a dense medium speeds up and bends towards the normal.

A light beam travelling from a rare medium to a dense medium slows down and bends away from the normal.

A light beam travelling from a rare medium to a dense medium speeds up and bends away from the normal.

Answer is Right!

Answer is Wrong!

This question was previously asked in

UPSC CDS-2 – 2023

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When a light beam travels from a rarer medium (lower refractive index, e.g., air) to a denser medium (higher refractive index, e.g., glass or water), its speed decreases. This change in speed causes the light ray to bend unless it is incident normally to the surface.

According to Snell’s Law of refraction (n₁ sin θ₁ = n₂ sin θ₂), where n₁ and n₂ are the refractive indices of the first and second media, and θ₁ and θ₂ are the angles of incidence and refraction respectively (measured from the normal). If light goes from a rarer medium (n₁) to a denser medium (n₂), then n₂ > n₁. For the equation to hold, sin θ₂ must be less than sin θ₁, which means θ₂ < θ₁ (for angles in the first quadrant). A smaller angle of refraction (θ₂) compared to the angle of incidence (θ₁) means the light ray bends towards the normal.

Conversely, when light travels from a denser medium to a rarer medium, its speed increases, and it bends away from the normal. Refractive index is defined as the ratio of the speed of light in vacuum to the speed of light in the medium (n = c/v). A denser medium has a higher refractive index and thus a lower speed of light.

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