Physics 9702 · AS & A Level · The diffraction grating

The diffraction grating — practice question

Light of wavelength $5.50 \times 10^{-7}\,\text{m}$ from a laser falls normally on a diffraction grating. The diffracted light then falls on a semicircular screen, as seen from above. In total, 9 bright dots appear on the screen. The grating is placed at the centre of the semicircle. The lines in the grating are vertical. The spacing between neighbouring lines in the grating is $d$. What could be a possible value of $d$?

  • A$2.25 \times 10^{-6}\,\text{m}$
  • B$2.80 \times 10^{-6}\,\text{m}$
  • C$4.40 \times 10^{-6}\,\text{m}$
  • D$4.95 \times 10^{-6}\,\text{m}$

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