Physics (AS & A Level) · Oct / Nov 2021 · Paper 13 · Question 30

A ray of green light is incident normally on a diffraction grating. Several bright spots are produced on a screen on the other side of the grating, as shown. Which pair of changes could result in bright spots at exactly the same angles as previously?

1. AUse blue light and increase the distance between the grating and the screen.
2. BUse blue light and increase the number of lines per unit length in the grating.
3. CUse red light and increase the distance between the grating and the screen.
4. DUse red light and increase the number of lines per unit length in the grating.

As printed in the paper