Back to Daily Question archive

AS Daily A Level Physics question

2026-06-17 OCR A Waves & optics (M4.2.2) OCR A Physics, Module 4: Electrons, waves and photons 4.2.2 Refraction, diffraction and interference (Young double-slit; fringe spacing trends) 4.2.1 Waves (phase difference and path difference underpinning interference)

In a school lab, a green laser produces a double-slit interference pattern on a screen 2.0 m away. The double-slit slide is replaced with one where the slit separation is half the original, while slit widths and the wavelength are unchanged. What happens to the spacing between adjacent bright fringes on the screen?

  1. A It decreases to 0.50× the original spacing.
  2. B It decreases to 0.25× the original spacing.
  3. C It stays the same.
  4. D It increases to 2.0× the original spacing. (correct)

Answer

The correct answer is D.

Correct: D — It increases to 2.0× the original spacing. With screen distance and wavelength fixed, fringe spacing is inversely proportional to slit separation, so halving the separation doubles the spacing. A says it decreases by a factor of 2, which reverses the inverse relationship. B assumes a squared dependence on separation, which is incorrect for fringe spacing. C claims no change, ignoring that separation directly sets the fringe spacing. D correctly applies the inverse proportionality: 1/(0.5) = 2.

Try today's guest Daily MCQ A Level Physics MCQ practice Problem-solving previews