Two slits are made 1 mm apart and the screen is placed 1 m away. What is the fringe width when a light used of wavelength 500 nm?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 0.5 mm
In Young’s double-slit experiment the fringe width is \( \beta = \lambda D/d \).
\( \lambda = 500\,\mathrm{nm} = 5\times10^{-7}\,\mathrm{m},\quad D = 1\,\mathrm{m},\quad d = 1\,\mathrm{mm} = 10^{-3}\,\mathrm{m} \)
\( \displaystyle \beta = \frac{5\times10^{-7}\times1}{10^{-3}} = 5\times10^{-4}\,\mathrm{m} = 0.5\,\mathrm{mm} \)
Note: A similar question was also asked in CUET (UG) 2025 on 29-05-2025 (Slot 2), and in CUET (UG) 2023 on 26-05-2023 (Slot 1).