Physics (AS & A Level) · Feb / March 2021 · Paper 12 · Question 29

A beam of red laser light of wavelength 633 nm is incident normally on a diffraction grating with 600 lines per mm. The beam of red light is now replaced by a beam of blue laser light of wavelength 445 nm. A replacement diffraction grating is used so that the first-order maximum of the blue light appears at the same position on the screen as the first-order maximum of the red light from the original laser. How many lines per mm are there in the replacement diffraction grating?

1. A420 mm⁻¹
2. B470 mm⁻¹
3. C600 mm⁻¹
4. D850 mm⁻¹

As printed in the paper