In a Young’s double‑slit experiment, the slit separation is $0.30,\text{mm}$ and monochromatic light of wavelength $550,\text{nm}$ is used. The screen is placed $2.0,\text{m}$ from the slits. Calculate the fringe spacing $\beta$ (distance between two consecutive bright fringes) on the screen.

Step-by-step solution

1. Use $\beta =\frac{Llambda}{d}$ where $L=2.0,\text{m}$, $\lambda =550\times 10^{-9},\text{m}$ and $d=0.30\times 10^{-3},\text{m}$.
2. Compute numerator: $Llambda=2.0\times 550\times 10^{-9}=1.10\times 10^{-6},{\text{m}}^2$.
3. Divide by $d$: $\beta =\frac{1.10\times 10^{-6}}{0.30\times 10^{-3}}\approx 3.67\times 10^{-3},\text{m}$.
4. Express in millimetres: $\beta \approx 3.67,\text{mm}$.

Concept tested: Young’s fringe spacing

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