CAPE Physics Unit 1 · 2008 · Paper 2 · Question 5(a)(iii)

A diffraction grating is illuminated by a parallel beam of light with a mixture of three wavelengths (yellow, blue, red) as shown in Figure 4, producing a spectrum with beams O, A, B, C.

Why does the central beam (labelled O) contain a mixture of all three colours?

This question uses a figure or table from the paper — you'll see it when you practise.