1.

A light ray is incident perpendicular to one face of a 90^@ prism and is totally internally reflected at the glass-air interface. If the angle of reflection is 45^@, we conculde that for the refractive index n as

Answer»

`nlt (1)/(root_2)`
`ngt root_2`
`ngt (1)/(root_2)`
`nlt root_2`

Solution :ACCORDING to condition of TOTAL internal reflection,
i = C where i = incidence angle, C = CRITICAL angle
`therefore sini gt sinC`
`therefore sini gt 1/N` [`becausen=(1)/(sinC)]`
`thereforen gt (1)/(sini)`
`therefore n gt (1)/(sin45^@)""[becausei=45^@]`
`therefore n gt sqrt2""[becausesin45^@=(1)/(sqrt2)`


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