Question

A light with a second-order bright band forms a diffraction angle of 30.0°. The diffraction grating has 250.0 lines per mm.

What is the wavelength of the light?

800 nm
1,000 nm
1,386 nm
1,732 nm

Answer 1

Use d sinθ = mλ. With 250 lines/mm, d = 1/250 mm = 4.0×10^−6 m. So

λ = d sin30° / 2 = (4.0×10^−6)(0.5)/2 = 1.0×10^−6 m = 1000 nm.

Answer: 1,000 nm.