An electron, at rest, has mass m_e and charge –q.
A positron is a particle that, at rest, has mass m_e and charge +q.
A positron interacts with an electron. The electron and the positron may be considered to be at rest.
The outcome of this interaction is that the electron and the positron become two gamma-ray (γ-ray) photons, each having the same energy.

Q: What topic does this question test?

This question tests Particle physics in A-Level Physics (syllabus code 9702). It is worth 6 marks.

Q: Which exam paper is this question from?

This question appeared in the Cambridge A-Level Physics May/June 2020 examination, Paper 4 Variant 3 (9702_s20_qp_43.pdf).

Question

An electron, at rest, has mass m_e and charge –q.
A positron is a particle that, at rest, has mass m_e and charge +q.
A positron interacts with an electron. The electron and the positron may be considered to be at rest.
The outcome of this interaction is that the electron and the positron become two gamma-ray (γ-ray) photons, each having the same energy.

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