Physics 9702 · AS & A Level · The diffraction grating

The diffraction grating — practice question

A beam of light is composed of two wavelengths, $436\,\text{nm}$ and $654\,\text{nm}$. A diffraction grating with $5.00 \times 10^{5}\,\text{lines m}^{-1}$ forms a diffraction pattern in which the second order for one wavelength appears at the identical angle $\theta$ as the third order for the other wavelength. What is the angle $\theta$?

  • A$19.1^{\circ}$
  • B$25.8^{\circ}$
  • C$40.8^{\circ}$
  • D$78.8^{\circ}$

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