In Fraunhofer diffraction experiment, $L$ is the distance between screen and the obstacle, $b$ is the size…
In Fraunhofer diffraction experiment, $L$ is the distance between screen and the obstacle, $b$ is the size of obstacle and $\lambda$ is wavelength of incident light. The general condition for the applicability of Fraunhofer diffraction is
$\frac{b^2}{L \lambda} \gg 1$
$\frac{b^2}{L \lambda}=1$
$\frac{b^2}{L \lambda} \ll 1$
$\frac{b^2}{L \lambda} \neq 1$
Solution
The general condition for Froun hofer diffraction is $\frac{b^2}{L \lambda} \ll 1$.