Fundamental interactions and exchange particlesAQA A-Level Physics: Subtopic test

1. 1
   Two electrons are fired towards each other in an evacuated chamber and are observed to repel one another.

   (a)

   Which exchange particle is responsible for the force between the two electrons?

   [1 mark]

   • AW⁺ boson
   • BW⁻ boson
   • CVirtual photon
   • DElectron neutrino

   (b)

   How does the exchange particle cause the electrons to repel each other?

   [1 mark]

   • AIt carries charge from one electron to the other
   • BIt is absorbed by the walls of the chamber
   • CIt changes one electron into a positron
   • DIt transfers momentum from one electron to the other

   (c)

   Explain why the repulsion between two electrons cannot be due to the exchange of a W⁻ boson.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Fluorine-18, used in medical imaging, decays by beta-plus emission. In its nucleus a proton changes into a neutron.

   (a)

   Which other particle is emitted in this decay, along with the positron?

   [1 mark]

   • AElectron antineutrino
   • BElectron neutrino
   • CElectron
   • DAntiproton

   (b)

   Which is the exchange particle in this decay?

   [1 mark]

   • AW⁺ boson
   • BW⁻ boson
   • CVirtual photon
   • DPositron

   (c)

   Write the equation for the decay of the proton in the nucleus and show that charge is conserved.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   In a heavy nucleus an inner-shell electron is captured by a proton, which changes into a neutron.

   (a)

   Describe electron capture in terms of the fundamental interaction and the exchange particle involved, and give the equation for the process.

   [3 marks]

   (b)

   A student states that the same reaction can occur when a high-energy electron collides with a proton in a particle accelerator. Evaluate this statement, including the interaction involved, the exchange particle and a check on charge conservation.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A neutron outside a nucleus is unstable and decays into a proton, whereas a proton is stable. Nuclei with too many neutrons undergo beta-minus decay, and nuclei with too many protons undergo beta-plus decay or electron capture.

   (a)

   Explain, in terms of the fundamental interactions and exchange particles, how a neutron decays into a proton in beta-minus decay. Include the equation and a charge check, and say why the electromagnetic and gravitational interactions are not responsible.

   [6 marks]

   (b)

   Compare beta-minus decay, beta-plus decay and electron capture in terms of the change in the nucleon, the exchange particle and the particles emitted.

   [6 marks]

   Total for question 4: 12 marks

End of questions