A beam of light consists of a continuous range of wavelengths from 420 nm to 740 nm. The light passes through a cloud of cool gas, as shown in Fig. 11.1. [Figure 11.1]

1. (a)The spectrum of the light emerging from the cloud of cool gas is viewed using a diffraction grating. Explain why this spectrum contains a number of dark lines.[4]
2. (b)(i)Light of wavelength 420 nm has a photon energy of 2.96 eV. Calculate the photon energy, in eV, of light of wavelength 740 nm.[2]
3. (b)(ii)Use data from (i) and your answer in (i) to show, on Fig. 11.2, the changes in energy levels giving rise to the dark lines in (a). [Figure 11.2 (not to scale)][2]

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