Light waves emerging from the slits of a diffraction grating are coherent and produce an interference pattern. A narrow beam of light from a laser is incident normally on a diffraction grating, as shown in Fig. 5.1. [Figure 5.1] Spots of light are seen on a screen positioned parallel to the grating. The angle corresponding to each of the second order maxima is 51°. The number of lines per unit length on the diffraction grating is 6.7 x 10⁵m⁻¹.

Q: What topic does this question test?

This question tests Superposition in A-Level Physics (syllabus code 9702). It is worth 5 marks.

Q: Which exam paper is this question from?

This question appeared in the Cambridge A-Level Physics Oct/Nov 2019 examination, Paper 2 Variant 3 (9702_w19_qp_23.pdf).

Question

Light waves emerging from the slits of a diffraction grating are coherent and produce an interference pattern. A narrow beam of light from a laser is incident normally on a diffraction grating, as shown in Fig. 5.1. [Figure 5.1] Spots of light are seen on a screen positioned parallel to the grating. The angle corresponding to each of the second order maxima is 51°. The number of lines per unit length on the diffraction grating is 6.7 x 10⁵m⁻¹.

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