Question

Show graphically the intensity distribution in Fraunhofer's single slit diffraction experiment. Label the axes.

Answer 1

Fraunhofer diffraction due to a single slit: Consider a monochromatic parallel beam of light of the wavelength ${\displaystyle \lambda }$ falling on a narrow slit of width ${\displaystyle a}$ as shown in the figure. A diffraction pattern is formed on the screen placed in the focal plane of the convex lens. Let ${\displaystyle O}$ be the centre of the slit and ${\displaystyle P_o}$ be the central
point of the screen. The rays extending from the slit on either side ${\displaystyle O{P}_o}$ are at equal optical paths from ${\displaystyle P_o}$ The maximum intensity is observed at central point ${\displaystyle P_o}$. It is called the principal maximum.

As ${\displaystyle \theta }$ increases, the intensity changes between alternate minima and maxima.

The condition for minima is ${\displaystyle a\sin \theta =n\lambda }$ where n = 1,2,3,4....

The condition for minima is ${\displaystyle a\sin \theta =(2n+1)\lambda \text{/}2}$ where n = 1,2,3,4....