Question

Write any two points of difference between interference pattern due to double-slit and diffraction pattern due to single-slit.

Hint:

Quick memory trick:

Interference → two sources, equal fringes
Diffraction → one slit, broad central maximum

Answer 1

Concept: Interference and diffraction are both wave phenomena, but they differ in origin and characteristics. Differences:

Origin:

Interference: Produced by superposition of light from two coherent sources (double slit).
Diffraction: Produced by superposition of wavelets from different parts of the same slit (single slit).

Fringe width and intensity:

Interference: Fringes are equally spaced and of nearly equal intensity (except due to envelope effects).
Diffraction: Central maximum is widest and brightest; secondary maxima are weaker and not equally spaced.

Other valid differences (any two acceptable):

Interference needs two slits; diffraction can occur with a single slit.
In interference, bright and dark fringes are sharp; in diffraction, intensity gradually decreases away from centre.