A monochromatic light of wavelength $480,\text{nm}$ falls normally on a diffraction grating with line spacing $1.5,\mu \text{m}$. Find the angle $\theta$ (in degrees) at which the second order ($m=2$) maximum is observed.

Step-by-step solution

1. Use the grating equation $dsin\theta =mlambda$ where $d=1.5\times 10^{-6},\text{m}$, $m=2$ and $\lambda =480\times 10^{-9},\text{m}$.
2. Compute $sin\theta =\frac{2\times 480\times 10^{-9}}{1.5\times 10^{-6}}=0.64$.
3. Take $\theta =si{n}^{-1}(0.64)\approx 39.8^{\circ }$, round to $40^{\circ }$.
4. Hence the second order maximum appears at about $40^{c}irc$.

Concept tested: Grating angular positions

Published 13 September 2026 · Last updated 16 September 2026 · How this solution was prepared and checked