(a)[4]
The spectrum of the light leaving the cloud of cool gas is observed with a diffraction grating. Explain why this spectrum has several dark lines.
(b(i))[2]
Light with wavelength $420\,\text{nm}$ has a photon energy of $2.96\,\text{eV}$. Calculate the photon energy, in $\text{eV}$, for light with wavelength $740\,\text{nm}$.
(b(ii))[2]
Use the data from (i) together with your answer in (i) to show, on Fig. 11.2, the changes in energy levels that produce the dark lines in (a).