A light ray from air is incident (as shown in figure ) at one end of a glass fiber ( refractive index `mu=1.5)` making an incidence angle of `60^(@)` on the lateral surface, so that it undergoes a total internal reflection. How much time would it take to traverse the straight fiber of length `1 km `?

Options

A. 3.33 `mu` s
B. 6.67`mu`s
C. 5.77 `mu`s
D. 3.85 `mu`s

Answer

D

Explanation

`sin i_(c ) = (1)/(n) rArr n = (1)/(sin i_(c )) = (2)/(sqrt(3))`
Time (t) = `("Distance")/("Velocity") = (nx)/(c )`
`= ((2)/(sqrt(3)) xx 10^(3) )/(3 xx 10^(8)) = 3.85 xx 10^(-6) " sec " rArr t = 3.85 mu `s.