Question

In Young's double slit experiment, yellow light of wavelength 640 nm produces fringes of width 0.8 mm. What will be the fringe width if the light source is replaced by another monochromatic source of wavelength 720 nm and the separation between the slits is made thrice?

• A. 2.4 mm
• B. 2.7 mm
• C. 0.3 mm
• D. 0.03 mm

Hint:

The fringe width in Young's double slit experiment is directly proportional to the wavelength and inversely proportional to the slit separation.

Answer 1

The Correct Option is A

The fringe width in Young's double slit experiment is given by: \[ w = \frac{\lambda D}{d} \] Where: - \(\lambda\) is the wavelength of light, - \(D\) is the distance between the screen and the slits, - \(d\) is the separation between the slits. When the wavelength changes and the slit separation is tripled, the new fringe width becomes: \[ w_{\text{new}} = \frac{720 \times D}{3d} = 3 \times \frac{640 \times D}{d} = 3 \times 0.8 \, \text{mm} = 2.4 \, \text{mm} \]