Conservation laws, mass-energy and antimatterEdexcel International A Level Physics: Flashcards

What these 14 flashcards ask

Which three quantities are conserved in particle interactions in this topic?
Write the mass-energy equation.
What is 1 MeV in joules?
What is 1 GeV in joules?
How do you convert a mass in MeV/c² to kg?
What is the rest energy of an electron?
What is an antiparticle?
What is pair production?
What is the minimum photon energy for electron-positron pair production?
Why does annihilation of a slow electron and positron give two photons?
Why do positive and negative particles curve in opposite directions in a magnetic field?
Why are high energies needed to investigate the structure of the proton?
What happens to the lifetime of an unstable particle moving at nearly the speed of light?
When is the relativistic increase in lifetime significant?

Exam questions on Conservation laws, mass-energy and antimatter

An electron and a positron, both moving very slowly, annihilate to produce two gamma-ray photons. The rest mass of an electron or of a positron is 0.511 MeV/c².
Describe what happens to the mass of the electron and the positron in the annihilation and how energy is conserved.2 marks
A gamma-ray photon of energy 2.50 MeV passes close to a nucleus in a bubble chamber and produces an electron-positron pair. The chamber is in a uniform magnetic field. The recoil of the nucleus may be ignored.
Calculate the total kinetic energy of the electron and positron.2 marks
Particle physicists quote the masses of particles in MeV/c² or GeV/c². A muon has a mass of 105.7 MeV/c². A proton and an antiproton each have a mass of 0.938 GeV/c². Use 1 eV = 1.60 × 10⁻¹⁹ J and c = 3.00 × 10⁸ m s⁻¹.
Calculate the mass of the muon in kg.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).