AQA ยท A level Physics

Early galaxy hydrogen ionisation A-level challenge

Can you get 100%? Use an early Hubble galaxy to test photon energy, hydrogen ionisation, redshift and why ultraviolet escape changed the Universe.

Read how an early galaxy clears hydrogen fog

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Question

8 marks

Answer all parts. Show your working and give units where appropriate.

1(a)

The ionisation energy of a hydrogen atom in its ground state is 13.6 eV. Calculate the minimum photon frequency that can ionise the atom. Use 1 eV = 1.60 x 10^-19 J and h = 6.63 x 10^-34 J s.

[3 marks]

1(b)

Young stars produce many ultraviolet photons. Explain how photons escaping from early galaxies could make the surrounding neutral hydrogen gas more transparent to later light.

[3 marks]

1(c)

The galaxy emitted ultraviolet light, but an Earth-orbiting telescope may detect some of that light at much longer wavelengths. Explain why.

[2 marks]

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