Question

If a diffraction grating has 3700 lines per cm, what is the spacing d between lines

Answer 1

so first we find the gap between the slits by the formula d=1/N

N is number of lines per metre so 3700 line/cm = 370000 lines/m
So d=2.7*10^-6

Now we use the formula dsin(angle)=n(wavelength)

d is the same
n is the order of the diffraction pattern

so wavelenth=dsin(angle)/n
=[(2.7*10^-6)*sin30]/3
=4.5*10^-7 m