Physics (AS & A Level) · Oct / Nov 2019 · Paper 11 · Question 28

Light of wavelength 720 nm from a laser X is incident normally on a diffraction grating and a diffraction pattern is observed. Light from a laser Y is then also incident normally on the same grating. The third-order maximum due to laser Y is seen at the same place as the second-order maximum due to laser X. What is the wavelength of the light from laser Y?

1. A480 nm
2. B540 nm
3. C720 nm
4. D1080 nm

As printed in the paper