Topic 1
Motion, forces, and energy — from vectors and kinematics to momentum, energy, and pressure.
OBJECTIVES:
By the end of this section, you will be able to :
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Helium nuclei (2 protons + 2 neutrons), charge +2e, mass ? 4u; strongly ionising, low penetration.
Positively charged particles in the nucleus; relative charge +1, relative mass ? 1.
Neutral particles in the nucleus; relative charge 0, relative mass ? 1.
Negatively charged particles around the nucleus; relative charge ?1, relative mass ? 1/1836.
Atoms/molecules that have lost one or more electrons, giving a net positive charge.
The splitting of a heavy nucleus into lighter nuclei plus neutrons, releasing energy.
Number of protons in the nucleus; determines the element.
Total number of protons + neutrons in the nucleus.
Charge compared with the proton’s charge magnitude: p = +1, e = ?1, n = 0.
Mass compared on a common scale (? proton mass): p ? 1, n ? 1, e ? 1/1836.
Atoms of the same element (same Z) with different numbers of neutrons (different A).
Low-level ionising radiation always present from natural and man-made sources (e.g. cosmic rays, rocks, radon, medical).
Radiations that can remove electrons from atoms/molecules (e.g. alpha, beta, gamma).
Emission of alpha particles; strongly ionising, very low penetration (stopped by paper/skin).
Emission of beta particles (electrons or positrons); moderate ionisation; stopped by a few mm of aluminium.
High-energy electromagnetic waves from the nucleus; weakly ionising but highly penetrating; reduced by thick lead/concrete.
The ability of radiation to create ions by knocking electrons out of atoms, leading to chemical/biological changes.
Comparative ability to pass through materials: ? low < ? medium < ? high.
Spontaneous, random change of an unstable nucleus to a more stable one with emission of radiation.
Nucleus emits an alpha particle; mass number ?4, atomic number ?2.
Typically ??: a neutron becomes a proton + electron + antineutrino; atomic number +1, mass number unchanged. (?? is the opposite change.)
Excited nucleus emits a gamma ray; proton and nucleon numbers unchanged.
Balanced nuclear equations showing parent ? daughter + emitted particle(s), conserving nucleon number and proton number.
The time for the activity (or number of undecayed nuclei) in a sample to fall to half its initial value.
Changes in the DNA of a cell; ionising radiation can increase the mutation rate. Some mutations are harmful (e.g. cancer), some neutral or rarely beneficial.
Motion, forces, and energy — from vectors and kinematics to momentum, energy, and pressure.
Thermal physics — particle model, temperature scales, specific heat capacity and heat transfer.
Waves — general properties, reflection/refraction, TIR, lenses and the EM spectrum.
Electricity and magnetism — charge, current, circuits, electrical power and safety.
Earth & Solar System, stars and the universe — redshift, CMBR, life cycle of stars and more.
Nuclear model, ionising radiation, decay equations and half-life.
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