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. $\frac{b^2}{L\lambda }\ne 1$

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 $\frac{b^2}{L\lambda }\ll 1$