Question

how many orders will be observed by a grating having 4000lines per cm if it is illuminated by light of wavelength in the range 5000A to 7500A

Answer 1

Answer:

Grating equation is (a+b) sinθ =nλ , N= 4000 lines/cm

For maximum orders sinθ = 1

Therefore , nmax=(a+b)λ=1Nλ

For 5000 Å, nmax=14000×5000×10−8=5.

For 7500 Å, nmax=14000×7500×10−8=3

So, in the wavelength range, 5000 to 7500 Å ,the observed number of orders range between 3 to 5

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