The refractive indices of water and glass with respect to air are 4/3 and 3/2 respectively. If the speed of light in glass is 2 × 108 ms-1, find the speed of light in (i) air, (ii) water.
(i) Let v1 = speed of light in air, v2 = speed of light in glass, then, n2n1 = refractive index of glass with respect to air = 32 v1v2=n2n1 , v2 = 2 × 108 m/s n1n2 = 23 v1 = 32 × 2 × 108 m/s = 3 × 108 m/s (ii) Let = speed of light in water, v2 = speed of light in air, then n2n1 = refractive index of water with respect to air v1v2=n2n1 Here, u2 = 3 × 108 m/s = n1n2 = 43 v1 = 34 × 3 × 108 = 1.5 × 108 m/s.
