The fringe width is 3.5 mm in Young's double slits experiment for a light of wavelength 700 nm. The fringe width for a light of wavelength 500 nm is:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 2.5 mm
In Young's double-slit experiment the fringe width is \( \beta = \lambda D/d \). The slit separation d and the screen distance D are unchanged, so \( \beta \) is directly proportional to \( \lambda \).
\( \displaystyle \frac{\beta_2}{\beta_1} = \frac{\lambda_2}{\lambda_1} \)
\( \displaystyle \beta_2 = 3.5\,\mathrm{mm}\times\frac{500\,\mathrm{nm}}{700\,\mathrm{nm}} = 2.5\,\mathrm{mm} \)