Intensity and Position of Secondary maxima

⁣According to Huygen Fresnel, every point of the wavefront in the plane of the slit is a source of secondary wavelets. ... The intensity at the point P1 is either minimum or maximum and depends upon the path difference between the secondary waves originating from the corresponding points of the wavefront.

PDF: ⁣https://drive.google.com/file/....d/1DgwEFggPpCbDPIKVZ