Question

In Fraunhoffer 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 Fraunhoffer diffraction is:

• A. $\frac{b^2}{l\lambda }>>1$
• B. $\frac{b^2}{l\lambda }=1$
• C. $\frac{b^2}{l\lambda }<<1$
• D. $\frac{b^2}{l\lambda }\ne 1$

Answer 1

The correct option is C $\frac{b^2}{l\lambda }<<1$

Fraunhofer diffraction is a far field effect.
It occurs when $\frac{b^2}{l\lambda }<<1$
where:

$b$ is size of obstacle

$\lambda$ is wavelength

$l$ is distance between screen and the obstacle.