Question

Two narrow parallel slits illuminated by a coherent monochromatic light produces an interference pattern on a screen placed at a distance $ D $ from the slits. The separation between the dark lines of the interference pattern can be increased by

• A. decreasing the distance between the screen and the slits
• B. increasing the distance between the slits
• C. using monochromatic light of a longer wavelength
• D. using monochromatic light of higher frequency

Hint:

The separation between the interference fringes is directly proportional to the wavelength of the light. A longer wavelength will result in a greater fringe separation.

Answer 1

The Correct Option is C

The separation between the dark lines in an interference pattern is given by the formula: \[ \Delta y = \frac{\lambda D}{d} \] Where: - \( \Delta y \) is the separation between the dark lines, - \( \lambda \) is the wavelength of the monochromatic light, - \( D \) is the distance between the slits and the screen, - \( d \) is the distance between the slits. From the formula, it is evident that the separation between the dark lines \( \Delta y \) is directly proportional to the wavelength \( \lambda \). 
Thus, to increase the separation between the dark lines, we can increase the wavelength \( \lambda \). 
Therefore, using monochromatic light of a longer wavelength will increase the separation between the dark lines of the interference pattern.