Discussion Forum

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 the slab is the same as to travel through a glass slab. The distance of the source  from the surface is 

Answer:

Explanation:

 Time taken by light to cross the glass slab,

 t= Distance/ speed of light in glass

 =  $\frac{5\times 10^{-2}}{\frac{3}{1.6}\times 10^{5}}s=2.67 \times 10^{-10}s$

In same time distance travelled by light in air

   =c x t= 3 x10⁸  x 2.67 x 10^-10

 =8.02 x 10^-2 m= 8 cm