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 m sec`
B. `6.67 m sec`
C. `5.77 m sec`
D. `3.85 mu sec`

Answer

D

Explanation

When total internal reflection just take place from lateral surface `i=C` i.e., `60^(@)=C`
`implies sin 60^(@)=sin C=(1)/(mu)impliesmu=(2)/(sqrt(3))`
Time taken by light to traverse some distance in a medium `t=(mu x)/(c)=((2)/(sqrt(3))xx10^(3))/(3xx10^(8))=3.85mu sec.`