Question

In interference pattern, using two coherent sources of light; the fringe width is ___________.

• A. directly proportional to wavelength.
• B. inversely proportional to square of the wavelength.
• C. inversely proportional to wavelength.
• D. directly proportional to square of the wavelength.

Answer 1

Answer: (A)

directly proportional to wavelength.

To obtain an interference pattern, we need a monochromatic light with two sources of same frequency and with constant phase difference, i.e. coherent sources. We also need a screen for observation.

The distance between the screen and the source is denoted as $D.$

The distance between the two sources is $d.$

Wavelength of light used is $\lambda .$

The width of each band of the pattern, fringe width, is $X.$

It is given by $X=\frac{\lambda D}{d}$

Thus $X\propto \lambda$