Explain diffraction by a single slit.

(N/A) As shown in the figure,by placing a monochromatic light source at the focus of a convex lens,the light rays emerging from it become parallel,forming a plane wavefront that is incident on the slit $LN$.
According to Huygens' principle,every point on the plane wavefront within the slit acts as an independent source of secondary spherical wavelets. As these wavelets emerge from the slit,they undergo interference with each other. This superposition results in constructive and destructive interference patterns.
Consequently,a diffraction pattern consisting of bright and dark fringes is obtained on a screen placed at the focal plane of a second convex lens,as illustrated in the figure.