Diffraction Due to a Circular Aperture
Category : JEE Main & Advanced
When a circular aperture is placed in the path of a light beam, then following diffraction pattern is formed on the screen.
(1) If only one HPZ is allowed by the aperture then the resultant amplitude at P would be \[{{R}_{1}}\]which is twice the value of amplitude for the unobstructed wave front. The intensity would there fore be \[4{{l}_{0}},\] where \[{{l}_{0}}\]represents the intensity at point P, due to unobstructed wave front.
(2) If the first two HPZ's are permitted by aperture than the resultant intensity at the centre point P will be very small (as \[{{R}_{1}}-{{R}_{2}}\approx 0)\]. In this case the diffraction pattern consist of a bright circle of light with a dark spot.
(3) In general if number of HPZ's (n) passing through aperture is odd, then the central point will be bright and if n is even, central point will be dark.
(4) The central bright disc is known as Airy's disc.
(5) In the non axial region bright and dark diffraction rings are obtained. The intensity of bright diffraction rings gradually goes on decreasing whereas that of dark diffraction goes on increasing.
(6) The first dark ring obtained around the central bright disc is known as Airy's ring.
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