On which of the following factors angular fringe width does not depend?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → distance between slits and screen
The angular fringe width is the fringe width \( \beta = \lambda D/d \) divided by the slit-screen distance \( D \), so \( D \) cancels:
\( \displaystyle \theta = \frac{\beta}{D} = \frac{\lambda}{d} \)
It depends only on the wavelength and the slit separation.
Option (1) wavelength — Depends on it. \( \theta \propto \lambda \).
Option (2) distance between slits — Depends on it. \( \theta \propto 1/d \).
Option (3) ratio of wavelength and distance between slits — Depends on it. \( \theta \) is exactly the ratio \( \lambda/d \).
Option (4) distance between slits and screen — Does not depend on it. \( D \) cancels; moving the screen changes the linear fringe width \( \beta \) but not the angle.