Electrons in an atom can move between discrete energy levels by absorbing or emitting electromagnetic radiation.
The diagram below shows electron transitions P and Q between energy levels in a hydrogen-like atom.
(i) Describe the direction and the start and end points of an arrow that represents the transition of an electron when it is ionised from the lowest energy level.
(ii) Complete the sentences about the electron transitions in the diagram using words from the list below:
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absorbed
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emitted
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excited
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ionised
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higher than
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lower than
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the same as
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When an electron makes transition P, it is _______________, and electromagnetic radiation is _______________ by the atom.
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The frequency of electromagnetic radiation involved in transition Q is _______________ the frequency of electromagnetic radiation involved in transition P.
Line spectra provide astronomers with vital information about the motion and distance of distant galaxies.
The table below gives the wavelength of a specific hydrogen spectral line measured in a laboratory on Earth, as well as the wavelengths of the same line observed in the light from Galaxy X and Galaxy Y.
| Source | Wavelength of line (nm) |
|---|---|
| Laboratory on Earth | 486 |
| Galaxy X | 512 |
| Galaxy Y | 530 |
Explain how the data in the table can be used to compare the motion and distance of Galaxy X and Galaxy Y from Earth.