The refractive index of the core of an optical fibre is `mu_(2)` and that of the cladding is `mu_(1)` .The angle of incidence on the face of the core so that the light ray just under goes total internal reflection at the cladding is

Options

A. `sin^(-1)(mu_(1)/mu_(2))`
B. `sin^(-1)sqrt(mu_(2)^(2)-mu_(1)^(2))`
C. `sin^(-1)sqrt(mu_(2)-mu_(1))`
D. `sin^(-1)sqrt(mu_(1)^(2) + mu_(2)^(2))`

Answer

B

Explanation

`r+c=90impliessinr=cosc`
`sinc=mu_(2)/mu_(1),sint_(2)=mu_(1)/mu_(a)sinr`