Physics (AS & A Level) · May / June 2025 · Paper 12 · Question 29

A student uses a diffraction grating to determine the wavelength of visible light from a source. The diffraction grating has 300 lines per mm. The student measures the angle θ of each order n of the intensity maxima. A graph of n against sin θ is plotted. The line of best fit for the plotted points is shown and has gradient G. Which expression represents the wavelength, in m, of the visible light in terms of G?

1. A3 × 10^5 G
2. B3.3 × 10^–6 G
3. C3.3 × 10^–6 / G
4. D300 / G

As printed in the paper