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Physics (AS & A Level) · Oct / Nov 2018 · Paper 12 · Question 30

9702The diffraction grating

A parallel beam of monochromatic light of wavelength λ is incident normally on a diffraction grating G. The angle between the directions of the two second-order diffracted beams at P₁ and at P₂ is α, as shown. What is the spacing of the lines on the grating?

  1. A2λ / sin α
  2. Bλ / sin α
  3. C2λ / sin(α/2)
  4. Dλ / sin(α/2)

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Correct answer: C. 2λ / sin(α/2)

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