Question

Class X Sciences
[papers from previous years]

Light enters from air into a glass plate which has a
refractive index of 1.50. Calculate the speed of light in glass.
The speed of light in air is
ms-1.

Answer 1

Refractive index of a transparent medium is defined as the ratio of the Speed of light in vacuum to the speed of light in the medium.

   1.50 = speed of light in vacuum / speed of light in glass
        
Speed of light in glass = 3 * 10^8 m/sec  / 1.50 = 2 * 10^8 m/sec

Answer 2

Answer:

Refractive index of a medium (nm) = Speed of light in vacuum/Speed of light in the medium

Speed of light in vacuum (c) = 3 × 108 m/s

Refractive index of glass (ng) = 1.50

Speed of light in the glass (v) = Speed of light in vacuum/ Refractive index of glass

= c/ng

=3 × 108/1.50 = 2x 108 ms-1.