# Describe the Fraunhofer’s diffraction at n-single slit. Find out the expression for resultant intensity for Fraunhofer’s diffraction at n-single slit.

Answer:

*Fraunhofer diffraction by n slit*

Expand our previous discussion of diffraction from a single slit; the l is an array of N slits with each slit having width “b” (b separation between slits) i.e. center to center distance is “a”. We consider N identical slits, illuminated by an incident plane wave and determine the superposition field and irradiance at an observation point P located far from the slits (or lying in a lens focal plane).

###### Fraunhofer diffraction by n slit

Let we consider a *diffraction* grating having n number of slits. When a monochromatic light incident on grating having n number of parallel slits. Each slits having equal width l and separated by a opaque distance b. The grating element is defines as the sum of both l+b. Now we consider the amplitude Asinβ/β at angle q with the direction of propagation.