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

  $\frac{b^2}{L \lambda}=1$
• Correct answer
  C

  $\frac{b^2}{L \lambda} \ll 1$
• D

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

Hence, the correct answer is option: 'C'.