What is the time taken (in seconds ) to cross a glass of thickness 4 mm and `mu= 3` by light

Options

A. `4 xx 10^(-11)`
B. `2 xx 10^(-11)`
C. `16 xx 10^(-11)`
D. `8 xx 10^(-10)`

Answer

A

Explanation

`v_(g) = (c )/(n) = (3 xx 10^(8))/(3) = 10^(8)` m/s
Time = `("Distance")/("speed") = (4 xx 10^(-3))/(10^(8)) = 4 xx 10^(-11)` sec.