Question

How shall the pattern change when white light is used in Fraunhofer Diffraction instead of monochromatic light?

(a) The pattern will no longer be visible

(b) The shape of the pattern will change from hyperbolic to circular

(c) The colored pattern will be observed with a white bright fringe at the center

(d) The bright and dark fringes will change position

The question was asked in an interview.

My query is from Fraunhofer Diffraction topic in chapter Optics of Engineering Physics II

Answer 1

Correct option is (c) The colored pattern will be observed with a white bright fringe at the center

To elaborate: When white light is used instead of monochromatic light in Fraunhofer Diffraction, then the central maximum remains white as all seven wavelengths meet there in the same phase. The first minimum and second maximum will be formed by violet color due to its shortest wavelength while the last is due to the red color as it has the longest wavelength. Thus, a colored pattern is observed.

However, after the first few colored bands, the clarity of the band is lost, due to overlapping.