Question

in reference to diffraction gratings and diffraction patterns.

For gratings with larger number of lines per mm, how is the spread of the diffraction pattern affected? support your argument with theory.

Answer 1

Sol:

As the number of lines per mm the diffraction angle increases and hence the diffraction pattern will get resolved more having good angular spread.

This can be supported as

N sinθ= mλ

Where N is grating element , θ is diffraction angle , m is the order and λ is wavelength of light.

Now as lines per mm increases , N grating element will decrease and thus , sinθ = mλ/N

Increases hence θ increases upto a limit since sinθ cannot be greater then 1 , hence by increasing lines per mm we will get good diffraction pattern which is more resolved and sharp.