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Question
| A ray of light travels from a denser to a rarer medium. After refraction, it bends away from the normal. When we keep increasing the angle of incidence, the angle of refraction also increases till the refracted ray grazes along the interface of two media. The angle of incidence for which it happens is called critical angle. If the angle of incidence is increased further the ray will not emerge and it will be reflected back in the denser medium. This phenomenon is called total internal reflection of light. |
The critical angle of the pair of a medium and air is 30°. The speed of light in the medium is:
Options
1 × 108 ms−1
1.5 × 108 ms−1
2.2 × 108 ms−1
2.8 × 108 ms−1
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Solution
1.5 × 108 ms−1
Explanation:
θC = 30°
μ = `1/(sin θ_"C") = 1/(sin 30°)` = 2
μ = `"velocity of light in vacuum"/"velocity of light in the medium"`
or, 2 = `(3 xx 10^8)/"velocity of light in the medium"`
∴ Velocity of light in the medium = 1.5 × 108 ms−1
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