Correct option is (A) 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 λ.
The width of each band of the pattern, fringe width, is X.
It is given by X = \(\frac {\lambda D}d\)
Thus X ∝ λ.
