Question

The speed of light in substance X is 1.25 × 10⁸ m/s and that in air is 3 × 10⁸ m/s. The refractive index of this substance will be:

(a) 2.4
(b) 0.4
(c) 4.2
(d) 3.75

Answer 1

(a) 2.4

Refractive index = $\frac{\mathrm{Speed}\mathrm{of}\mathrm{light}\mathrm{in}\mathrm{air}}{\mathrm{Speed}\mathrm{of}\mathrm{light}\mathrm{in}\mathrm{the}\mathrm{substance}}$

=$\frac{3\times {10}^8\mathrm{m}/\mathrm{s}}{1.25\times {10}^8\mathrm{m}/\mathrm{s}}$ = 2.4