Question

In Young's double slit experiment, green light is incident on the two slits. The interference pattern is observed on a screen. Which one of the following changes would cause the observed fringes to be more closely spaced?

• A. Reducing the separation between the slits
• B. Using blue light instead of green light
• C. Using red light instead of green light
• D. Moving the screen away from the slits

Hint:

In double-slit experiments, the fringe spacing depends on the wavelength of the light. Longer wavelengths result in closer fringes.

Answer 1

The Correct Option is C

Step 1: Understanding the fringe spacing.
The fringe spacing in a double-slit experiment is given by the formula: \[ \Delta y = \frac{\lambda L}{d} \] where \( \lambda \) is the wavelength of the light, \( L \) is the distance between the slits and the screen, and \( d \) is the separation between the slits.

Step 2: Analyzing the options.
(A) Reducing the separation between the slits: This would increase the fringe spacing, not decrease it.
(B) Using blue light instead of green light: Blue light has a shorter wavelength, which would result in closer fringes.
(C) Using red light instead of green light: Red light has a longer wavelength, which results in closer fringes.
(D) Moving the screen away from the slits: This would increase the fringe spacing.

Step 3: Conclusion.
The correct answer is (C) Using red light instead of green light, as it will produce a longer wavelength and cause the fringes to be more closely spaced.