In an interference experiment, the two slits are 1 mm apart and the screen is placed 1 m away from the slits. The width of a bright fringe for the light of wavelength 500 nm is
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 0.5 mm
In Young's double-slit experiment the bright and dark fringes are equally wide, and each has the fringe width
\( \displaystyle \beta = \frac{\lambda D}{d} \)
\( \lambda = 500\,\mathrm{nm} = 5\times10^{-7}\,\mathrm{m} \)
\( D = 1\,\mathrm{m} \)
\( d = 1\,\mathrm{mm} = 10^{-3}\,\mathrm{m} \)
\( \displaystyle \beta = \frac{5\times10^{-7} \times 1}{10^{-3}} = 5\times10^{-4}\,\mathrm{m} = 0.5\,\mathrm{mm} \)
Note: A similar question was also asked in CUET (UG) 2023 on 13-06-2023 (Slot 3) and on 26-05-2023 (Slot 1).