Question

A diffraction grating is illuminated by a Laser light of wavelength 500 nm. If the second
order spectral line is observed at 30°, then the number of lines per centimetre of
grating is
(11 5000
(2) 6000
(3) 4000
(4) 3000​

Answer 1

Answer:

N = 4000 line/cm, λ = 5000 x10−8, n= 3

dθdλ=n(a+b)cosθ(a+b)sinθ=nλsinθ=nλ(a+b)sinθ=Nnλ [∵(a+b)=1N]sinθ=4000×3×5000×10−8=0.6θ=36.86

cosθ = 0.80

Therefore dispersive power dθdλ=Nncosθ=15000