Question

what happens if the no of line per cm in the Diffraction gratiing is halved ?​

Answer 1

Answer:

a+b is grating element, the distance between two consecutive slits. n is order of principal maxima,where we get the spectral lines. Lambda is wavelength of light. To understand the answer to your question , let us consider first order maximum on either side of central maximum. For first order n=1. Therefore ,sin (theta 1)= (lambda)/ (a+b).

Answer 2

There’s a good discussion of this in Wikipedia under “Diffraction Grating”. In brief, if the number of lines per cm in increased and thus the spacing of the lines d is decreased then the angle from the incident light where a given wavelength appears will increase. For example, the angle where the first red light appears will increase (be farther away from the incident light