Question

Light with a wavelength of about 510 nm is made to pass through a diffraction grating. The angle formed between the path of the incident light and the diffracted light is 12.0° and forms a first-order bright band.

The number of lines per mm in the diffraction grating, rounded to the nearest whole number, is
lines per mm.

Answer 1

Grating equation (normal incidence): d sinθ = mλ. For first order m = 1 and θ = 12.0°.

d = λ / sinθ = 510×10^−9 m / sin(12.0°) = 2.453×10^−6 m.

Lines per mm = 1/d (per m) ÷ 1000 = (1 / 2.453×10^−6) / 1000 ≈ 407 lines/mm.

Answer: 407 lines per mm.