Physics (AS & A Level) · May / June 2021 · Paper 11 · Question 29

Light of a single unknown wavelength and blue light of a single wavelength are both incident normally on a diffraction grating. Two diffraction patterns are produced, one for each wavelength of light. The third-order maximum for the blue light occurs at the same angle as the second-order maximum for the light of unknown wavelength. The wavelength of the blue light is 480 nm. What is the unknown wavelength?

1. A320 nm
2. B720 nm
3. C960 nm
4. D1440 nm

As printed in the paper