1.

A prism having refractive index 1.414 and refracting angle 30^(@) has one of the refracting surfaces silvered. A beam of light incident on the other refracting surface will retrace its path, if the angle of incidence is :

Answer»

`0^(@)`
`30^(@)`
`60^(@)`
`45^(@)`

SOLUTION :(d) At second surface, there is no refraction so `
r_(2) = 0`
`THEREFORE "" r_(1) = A = 30^(@)`
From Snell.s law
`n = (sin i_(1))/(sinr_(1))`
`n = (sin i_(1))/(sin 30)`
`sin i_(1) = SQRT(2) XX (1)/(2) = (1)/(sqrt(2))`
`sin i_(1) = (1)/(sqrt(2))`
`i_(1) = 45^(@)`


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