Question

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

• A. $\frac{b^{2}}{L \lambda } \gg 1$
• B. $\frac{b^{2}}{L \lambda } = 1$
• C. $\frac{b^{2}}{L \lambda } \ll 1$
• D. $\frac{b^{2}}{L \lambda } \neq 1$

Answer 1

Answer: (C)

The general condition for Fraunhofer diffraction Is that
$b\approx\lambda L>>bL>>\lambda \frac{b^{2}}{\lambda } < < L\frac{b^{2}}{\lambda L} < < 1$
The general condition for Fraunhofer diffraction is $\frac{b^{2}}{L \lambda }\ll1$