In a Young's double‑slit experiment the slit separation is $d=0.25\text{mm}$, the wavelength of the light is $\lambda =600\text{nm}$ and the screen is placed $L=1.5\text{m}$ from the slits. Calculate the distance $\beta$ between two successive bright fringes on the screen.

Step-by-step solution

1. Convert all quantities to metres: $d=0.25\text{mm}=2.5\times 10^{-4}\text{m}$, $\lambda =600\text{nm}=6.0\times 10^{-7}\text{m}$, $L=1.5\text{m}$.
2. Use the fringe spacing formula for Young's experiment: $\beta =\frac{\lambda L}{d}$.
3. Substitute the values: $\beta =\frac{6.0\times 10^{-7}\times 1.5}{2.5\times 10^{-4}}$.
4. Perform the calculation: numerator $=9.0\times 10^{-7}$, denominator $=2.5\times 10^{-4}$, so $\beta =3.6\times 10^{-3}\text{m}=3.6\text{mm}$.
5. State the result.

Concept tested: Young's double‑slit fringe spacing

Published 19 September 2026 · How this solution was prepared and checked