Physics 9702 · AS & A Level · The diffraction grating

The diffraction grating — practice question

A beam of red light with wavelength $720\,\text{nm}$ is directed normally onto a diffraction grating, creating a diffraction pattern on a screen that lies parallel to the grating. This red-light beam is then substituted by a beam of electromagnetic radiation with wavelength $X$, which also strikes the same diffraction grating at normal incidence. The third-order maximum for the radiation of wavelength $X$ appears at the same point on the screen as the second-order maximum for the red light. Determine wavelength $X$.

  • A$480\,\text{nm}$
  • B$540\,\text{nm}$
  • C$960\,\text{nm}$
  • D$1100\,\text{nm}$

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