A laser beam passes through a thin slit

PHYSICS · Single correct · A Level · Physics · Waves · Waves

Problem

A laser beam passes through a thin slit. When the pattern is viewed on a screen

1.25\ \text{m}

past the slit, the fifth-order dark fringes occur at

\pm2.41\ \text{cm}

from the central bright fringe. The experiment is then performed in a liquid, and each fifth-order dark fringe is

0.790\ \text{cm}

closer to the central fringe than it was in air. What is the refractive index of the liquid? (a) 1.33 (b) 1.40 (c) 1.49 (d) 1.62