A star in a distant galaxy consists mostly of hydrogen. Visible light emitted by the star consists of discrete spectral absorption lines, as represented in Figure 8.1.

Figure 8.1, four spectral absorption lines on a horizontal scale, at wavelengths 410 nm, 434 nm, 486 nm and 656 nm

The numbers represent the wavelengths, in nm, of the spectral lines. Explain, with reference to photons, how the existence of these spectral lines provides evidence for discrete electron energy levels in the hydrogen atom.

Answer

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8(b)(i)Redshift Expansion Big BangMedium2 marks

The galaxy is at a distance of

6.7 \times 1 0^{24} m

from the Earth. Explain why the spectral lines observed on the Earth are at different wavelengths from those shown in Figure 8.1.

Answer

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8(b)(ii)Redshift Expansion Big BangEasy2 marks

On Figure 8.1, draw possible positions for the four spectral lines observed on the Earth.

Draw with the mouse or a finger.

8(b)(iii)Redshift Expansion Big BangMedium3 marks

The Hubble constant may be taken as

2.1 \times 1 0^{- 18} s^{- 1}

. Determine the observed wavelength, in nm, of the lowest frequency spectral line of visible light from the star.