A diffraction grating has 500 lines per millimeter
PHYSICS · Single correct · A Level · Physics · Waves · Waves
Problem
A diffraction grating has 500 lines per millimeter. Determine whether the second-order maximum for blue light (λ = 450 nm) overlaps the first-order maximum for red light (λ = 650 nm).
(a) Yes; both maxima occur at approximately 19∘ from the central maximum, so the spectra overlap.
(b) Yes; because 2λblue≈λred, the two maxima coincide at the same angle.
(c) No; the second–order blue maximum appears at a larger angle than the first–order red maximum, so they remain distinct.
(d) No; neither maximum can occur because the required value of sinθ would exceed 1, therefore no overlap is possible.