Is there any relation between the incident light wavelength and the slit width.?

Question

In the case of a grating plate .... to get the better interference pattern number of lines per grating plate should be changed according to the incident wavelength. Is there any relation between these two.

Answer 1

The width pf entrance slit to the grating has nothing to do with the diffraction. The slit is only there so you can image it over and over again on your detector in different wavelengths.

It is the distance between the rulings on the grating (and some other things; see below) that determines the angle of diffraction.

It sounds to me like you are looking for a grating equation; the relationship between the line separation of the grating, the angle of incidence, angle of diffraction, order of the diffraction and the wavelength of the incident wave.

http://www.tau.ac.il/~phchlab/experiments/hydrogen/diffraction_gratings.htm

Answer 2

Sorry, your question makes no sense.