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प्रश्न
Define the critical angle for a given pair of media and total internal reflection. Obtain the relation between the critical angle and refractive index of the medium.
उत्तर
The angle of incidence corresponding to an angle of refraction of 90° is called the critical angle for the given pair of media. If the angle of incidence of light, when travelling from a denser medium to a rarer medium, is greater than the critical angle then total internal reflection takes place.
Let the angle of incidence i and C be the critical angle C.
Let the angle of refraction r = 90°.
The refractive index of the rarer medium is μa.
The refractive index of the denser medium is μb.
Applying Snell's law,
`(sini)/(sinr) = mu_a/mu_b`
μb sinC = μa sin90° ....[∵ i = C and r = 90°]
`mu_a/mu_b = 1/(sinC)`
Thus, we arrive at a formula expressing the critical angle and refractive index relation:
`""_amu_b = 1/(sinC)`
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