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Question
Show graphically the intensity distribution in Fraunhofer's single slit diffraction experiment. Label the axes.
Solution
Fraunhofer diffraction due to a single slit: Consider a monochromatic parallel beam of light of the wavelength `lambda` falling on a narrow slit of width `a` as shown in the figure. A diffraction pattern is formed on the screen placed in the focal plane of the convex lens. Let `O` be the centre of the slit and `P_o` be the central
point of the screen. The rays extending from the slit on either side `OP_o` are at equal optical paths from `P_o` The maximum intensity is observed at central point `P_o`. It is called the principal maximum.
As `theta` increases, the intensity changes between alternate minima and maxima.
The condition for minima is `a sin theta = nlambda` where n = 1,2,3,4....
The condition for minima is `a sin theta = (2n + 1)lambda"/"2` where n = 1,2,3,4....
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