CAIE A-Level Physics A2 24.3.5 The Energy of the Gamma Ray Photons Emitted During the Annihilation of an Questions

Practise calculating the total gamma-photon energy released when an electron and positron annihilate using E = 2mc², checking the particle masses and units.

Exam points

calculate the total energy of gamma photons from electron-positron annihilation using E = 2mc²

[Maximum number: 2]

An electron, at rest, has mass $m_{\mathrm{e}}$ and charge -q.
A positron is a particle that, at rest, has mass $m_{\mathrm{e}}$ 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 ( $\gamma$ -ray) photons, each having the same energy.

Calculate, for one of the $\gamma$ -ray photons:

the photon energy, in J
energy =

$E=m c^{2}$ $\begin{aligned} =9.11 \times 10^{-31} \times\left(3.0 \times 10^{8}\right)^{2} =8.2 \times 10^{-14} \mathrm{~J} \end{aligned}$

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CAIE A-Level Physics A2 24.3.5 The Energy of the Gamma Ray Photons Emitted During the Annihilation of an Questions question 1