Physics 9702 · AS & A Level · The diffraction grating

The diffraction grating — practice question

Monochromatic light of wavelength $720\,\text{nm}$ from laser X is directed normally at a diffraction grating, and a diffraction pattern is formed. Light from laser Y is then also directed normally at the same grating. The third-order maximum produced by laser Y appears at the same position as the second-order maximum produced by laser X. What is the wavelength of the light from laser Y?

  • A$480\,\text{nm}$
  • B$540\,\text{nm}$
  • C$720\,\text{nm}$
  • D$1080\,\text{nm}$

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