# In Fraunhoffer diffraction experiment , L is the distance between screen and the obstacle, b is the size of the obstacle and $\lambda$ is wavelength of incident light. The general condition for the applicability of Frauhoffer diffraction is

$\begin {array} {1 1} (1)\;\frac{b^2}{L \lambda} > > 1 & \quad (2)\;\frac{b^2}{L \lambda} = 1 \\ (3)\;\frac{b^2}{L \lambda} < < 1 & \quad (4)\;\frac{b^2}{L \lambda} \neq 1 \end {array}$

$(3)\;\frac{b^2}{L \lambda} &lt; &lt; 1$