Diffraction



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                  To determine the light intensity distribution for a single-slit diffraction pattern we can use phasors. Imagine a slit divided into a large number of small zones, each of width as shown in following figure.

              Each zone acts as a source of coherent radiation, and each contributes an incremental electric field of magnitude ΔE at some point P on the screen. We obtain the total electric field magnitude E at point P by summing the contributions from all the zones. The light intensity at point P is proportional to the square of the magnitude of the electric field The incremental electric field magnitudes between adjacent zones are out of phase with one another by an amount ∆β, where the phase difference ∆β is related to the path difference ∆y sinθ between adjacent zones by the expression,

Because the resultant light intensity I at point P on the screen is proportional to the square of the magnitude ER , we find that,