Energy, mass and antimatterEdexcel A-Level Physics: Flashcards
What these 13 flashcards ask
- State the three quantities that are always conserved in a particle interaction.
- What equation links mass change and energy change?
- How many joules are in 1 MeV?
- What does a mass of 938 MeV/c² mean?
- What is the minimum photon energy for electron–positron pair production?
- Why is pair production not seen for a photon in empty space?
- Why do an electron and positron at rest annihilate to give two photons, not one?
- How do an antiparticle and its particle differ?
- Why do the tracks of an electron and positron curve in opposite senses in a magnetic field?
- Why do high-energy electrons probe the inside of a nucleon?
- What approximation links momentum and energy for a very high-energy particle?
- When is the relativistic increase in particle lifetime significant?
- In which frame is the lifetime of an unstable particle shortest?
Exam questions on Energy, mass and antimatter
- In a positron emission tomography (PET) scanner, a positron emitted by a radioactive tracer in a patient annihilates with an electron in the surrounding tissue. Both particles can be taken to be at rest when they annihilate. The rest mass of an electron is 0.511 MeV/c².Calculate the energy, in MeV, of each photon produced.2 marks
- A gamma ray photon of energy 3.0 MeV, which leaves no track in a bubble chamber, converts into an electron and a positron close to an atomic nucleus. The chamber is in a uniform magnetic field and the two particles leave tracks that start at the same point. The rest mass of an electron is 0.511 MeV/c².Calculate the total kinetic energy of the electron and the positron, in MeV, immediately after the pair is created. Assume the nucleus takes negligible energy.2 marks
- Physicists fire a beam of electrons at liquid hydrogen to investigate the structure of the proton, which has a radius of about 1 × 10⁻¹⁵ m. At low beam energies the electrons scatter as if the proton were a single point. At very high beam energies some electrons are scattered through large angles, showing that the proton has internal structure.Explain why electrons of very high energy are needed to investigate the internal structure of the proton.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).