Question

Describe Young's double-slit interference experiment.

Answer 1

1. When a convex lens is focused on a linear source S of monochromatic light, two equally narrow slits, S₁ and S₂, are passed through to produce plane wavefronts. Presently, these two slits function as two coherent sources of newly generated cylindrical waves with a phase difference of zero or constant. As seen in the picture, a screen PQ is positioned parallel to S₁S₂ and at a certain distance from the double slits.
   
   Young’s double-slit experiment
2. As indicated by the dots \[\ce{(\bullet)}\] in the figure, the waves from S₁ and S₂ constructively interact at locations where they meet in phase, where a wave's crest superposes on another wave's crest, or where the two waves' troughs superpose. On antinodal lines are these dots located. Bright and intense dots appear on the screen along the antinodal lines.
3. In a similar vein, where the crest of one wave coincides with the trough of the other, the waves from S₁ and S₂ destructively interfere. The hollow circles (O) represent these spots, which are located on nodal lines. The screen's lowest intensity and darkest areas are found along the nodal lines.
4. The entire pattern is referred to as an interference pattern, and the dark and bright areas are referred to as fringes or bands.