Physics - Recall for Chapter 24: Particle Physics
OCR A-Level Physics 2022
Flashcards
Rutherford’s scattering experiment
What material was used as a target in Rutherford’s scattering experiment?
Gold foil.
How thick was the gold foil used in Rutherford’s scattering experiment?
Only a few atoms.
What was measured in Rutherford’s scattering experiment?
The angle of deflection of alpha particles.
What happened to most of the alpha particles in Rutherford’s scattering experiment?
They passed straight through the foil.
What proportion of alpha particles were scattered in Rutherford’s scattering experiment?
Around 1 in 2000.
What proportion of alpha particles were deflected by more than 90 degrees in Rutherford’s scattering experiment?
Around 1 in 10,000.
What was concluded to due to most of the alpha particles passing straight through the gold foil in Rutherford’s scattering experiment?
Most of the atom is empty space with most of the mass concentrated in a small nucleus.
What was concluded due to some alpha particles being scattered in Rutherford’s scattering experiment?
The nucleus is positively charged.
How did Rutherford estimate the maximum radius of the nucleus?
He equated the kinetic energy of the alpha particle to the electric potential at closest approach to the nucleus.
The nucleus and isotopes
What is an isotope?
A nucleus of an element with the same number of protons but a different number of neutrons.
What is an atomic mass unit?
One twelfth the mass of a neutral carbon-12 atom.
Measuring the nuclear radius
How has the radius of the nucleus been measured?
By the diffraction of fast-moving electrons.
What experiment gives a more accurate measure of the radius of an atom than Rutherford’s gold foil experiment?
Measuring the diffraction of fast-moving electrons.
The strong nuclear force
What force holds protons and neutrons together in the nucleus?
The strong nuclear force.
Below what distance is the strong nuclear force repulsive?
Fundamental particles, hadrons and leptons
What is a fundamental particle?
A particle that has no internal structure and is not composed of other particles.
What are three examples of fundamental particles?
- Electrons
- Quarks
- Neutrinos
What is a hadron?
A particle that experiences the strong nuclear force and is composed of two or more quarks.
Which group of particles are subject to the weak nuclear force but not the strong nuclear force?
Leptons.
Neutrinos
Why doesn’t a neutrino experience the electromagnetic force?
They have no charge.
Quark composition of nucleons
What is the family of particles that are subject to both the strong and weak nuclear force?
Hadrons.
Particles and antiparticles
How does a proton compare to an antiproton?
They have the same mass but opposite charge.
How does an electron compare to a positron?
They have the same mass but opposite charge.
What type of particle are there millions passing through your body every second?
Neutrinos.
Beta decay
Can you describe beta minus decay?
A neutron in an unstable nucleus decays into a proton and emits an electron and an antineutrino.
What is it easy to forget in describing beta decay?
The emission of a neutrino/antineutrino.
Can you describe beta plus decay?
A proton in an unstable nucleus decays into a neutron and emits a positron and a neutrino.
What quark transformation occurs during beta minus decay?
A down quark turns into an up quark.
What quark transformation occurs during beta plus decay?
An up quark turns into a down quark.