A ray of light is incident normally on a glass slab of thickness 5 cm and refractive index 1.6. The time taken to travel by a ray from source to surface of slab is same as to travel through glass slab. The distance of source from the surface is

Options

A. 4 cm
B. 8 cm
C. 12 cm
D. 16 cm

Answer

B

Explanation

Time taken by light to cross the glass slab,
`t=("Distance")/("Speed of light in glass")`
`=(5xx10^(-2))/((3)/(1.6)xx10^(8))s=2.67xx10^(-10)s`
In same time distance travelled by light in air
`=cxxt=3xx10^(8)xx267xx10^(10)`
`=8.02xx10^(-2)m~~8cm`