A light ray travels from air into water. The speed of light in air is 3.00×10^8 m/s and in water it is 2.25×10^8 m/s. Find the refractive index of water.

A light ray travels from air into water. The speed of light in air is $3.00 \times 1 0^{8} m/s$ and in water it is $2.25 \times 1 0^{8} m/s$ . Find the refractive index of water.

medium 2 marks Class 7 · Science · Light

Answer

1.333

The correct answer is 1.333 — Divide the numbers: $n = 1.333$ (to three significant figures).

The refractive index $n$ of a medium is given by $n = \frac{v _{air}}{v _{medium}}$ .
Substitute the given speeds: $n = \frac{3.00 \times 1 0 ^{8}}{2.25 \times 1 0 ^{8}} .$
Divide the numbers: $n = 1.333$ (to three significant figures).

Common mistake: Using the ratio

v_{medium} / v_{air}

instead of the correct one

Concept tested: Refractive index calculation