Light from a point source passes through a single slit and is then incident on a double-slit arrangement - AQA - A-Level Physics - Question 16 - 2018 - Paper 1

To determine which option will increase the fringe spacing in a double-slit interference pattern, it is essential to understand the formula for fringe spacing:

$y = \frac{\lambda D}{d}$

where:

• $y$ is the fringe spacing,
• $\lambda$ is the wavelength of the light,
• $D$ is the distance from the double slits to the screen, and
• $d$ is the distance between the slits.

1. Option A: Increasing the separation of the single slit and the double slit does not directly affect the interference fringe spacing.
2. Option B: Increasing the width of the single slit may alter the intensity of the light but does not directly increase fringe spacing.
3. Option C: Decreasing the distance between the double slits and the screen (D) would actually decrease the fringe spacing, according to the formula.
4. Option D: Decreasing the separation of the double slits (d) leads to an increase in fringe spacing.

Thus, the correct answer is D: decreasing the separation of the double slits.