In a double slit experiment, if the distance between the slits be reduced to half, then the new fringe width will be
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → doubled
The fringe width in a double slit experiment is
\( \displaystyle \beta = \frac{\lambda D}{d} \)
where \( d \) is the distance between the slits and \( D \) the distance of the screen. So \( \beta \) is inversely proportional to \( d \).
\( \displaystyle \beta' = \frac{\lambda D}{d/2} = 2\,\frac{\lambda D}{d} = 2\beta \)
The fringe width is doubled.
Note: The same question was also asked in CUET (UG) 2025 on 30-05-2025 (Slot 2).
NCERT (2026-27):
Interference of Light Waves and Young’s Experiment – “… Thus dark and bright bands appear on the screen, as shown in Fig. 10.13. Such bands are called fringes. Equations (10.18) and (10.19) show that dark and bright fringes are equally spaced and the distance between two consecutive bright and dark fringes is given by
\( \displaystyle \beta = x_{n+1} - x_{n} \quad \text{or} \quad \beta = \frac{\lambda D}{d} \qquad (10.20) \)
which is the expression for the fringe width.”