Light travels from air into glass slab of thickness 50 cm and refractive index 1.5.
(i) What is the speed of light in glass?
(ii) What is the time taken by the light to travel through the glass slab?
(iii) What is the optical path of the glass slab?

Explanation

Give: thickness of glass slab, d = 50 cm = 0.5 m, refractive index, n = 1.5
refractive index, `n = (c )/(v)`
speed of light in glass is, `v = (c )/(n) = (3 xx 10^(8))/(1.5) = 2 xx 10^(8) ms^(-1)`
Time taken by light to travel through slab is, `t = (d)/(v) = (0.5)/(2 xx 10^(8)) = 2.5 xx 10^(-7) s`
optical path, d. = nd = `1.5 xx 0.5 = 0.75 m = 75 cm`
LIght woul have travelled 25 cm more (75 cm - 50 cm) in vacuum by the same time had there been a glass slab.