The time required for the light to pass through a glass slab ( refractive index=1.5) of thickness u mm is (c=`3xx10^(8)ms^(-1)` speed of light in free space)

Options

A. `2xx10^(-5)s`
B. `2xx10^(11)s`
C. `2xx10^(-11)s`
D. `10^(-11)"s"`

Answer

C

Explanation

Refractive Index, `(n_(g))/(n_(a))=(c_(a))/(c_(g))`
`implies" "(3)/(2)=(3xx10^(8))/(c_(g))`
`c_(g)=2xx10^(8)`
`"Time"=("Distance")/("Speed")`
`=(4xx10^(-3))/(2xx10^(8))=2xx10^(-11)s`