Page 498 - Physics Coursebook 2015 (A level)

Cambridge International A Level Physics
8 Figure 30.28 shows five of the energy levels in a helium ion. The lowest energy level is known as the ground state.
–2.8 eV –3.4 eV –6.1 eV
–13.6 eV
–54.4 eV
Figure 30.28
n =5 n =4 n =3
n =2
n =1 (ground state) For End-of-chapter Question 8.
a Calculate the energy, in joules, that is required to completely remove the remaining electron,
originally in its ground state, from the helium ion. [2]
b Calculate the frequency of the radiation which is emitted when the electron drops from the level
n = 3 to n = 2. State the region of the electromagnetic spectrum in which this radiation lies. [2]
c Without further calculation, describe qualitatively how the frequency of the radiation emitted when
the electron drops from the level n = 2 to n = 1 compares with the energy of the radiation emitted whenitdropsfromn=3ton=2. [2]
9 The spectrum of sunlight has dark lines. These dark lines are due to the absorption of certain wavelengths by the cooler gases in the atmosphere of the Sun.
a One particular dark spectral line has a wavelength of 590 nm. Calculate the energy of a photon with
this wavelength. [3]
b Figure 30.29 shows some of the energy levels of an isolated atom of helium.
Energy / 10–19 J 0
–1.6
–2.4 –3.0
–5.8 –7.6
Figure 30.29 For End-of-chapter Question 9.
i Explain the significance of the energy levels having negative values. [1]
ii Explain, with reference to the energy level diagram above, how a dark line in the spectrum
may be due to the presence of helium in the atmosphere of the Sun. [2]
iii AllthelightabsorbedbytheatomsintheSun’satmosphereisre-emitted.Suggestwhya
dark spectral line of wavelength of 590 nm is still observed from the Earth. [1]
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