Question

A light ray enters a piece of transparent plastic with a thickness of 50 m and a refractive index of 1.2. What is the time taken by the ray to propagate through the plastic if the velocity of light in air is 3 x 10^8 ms^-1?

The options for the answer are 2.5 x 10^-8 s / 2.0 x 10^-8 s / 1.5 x 10^-7 s / 2.0 x 10^-7 s

Answer 1

t= 2*10⁻⁷ seconds

Step-by-step explanation:

Refractive index is given by the formula;

η= c/v where c= 3.0 * 10⁸ m/s speed of light and v is speed of light in plastic

substitute the values in the formula as;

1.2 = 3.0 * 10⁸/ v

3.0 * 10⁸ /1.2

v= 2.5 *10⁸ m/s

t= distance / speed

t= 50/2.5*10⁸

t= 2e⁻⁷ seconds

t= 2*10⁻⁷ seconds