Overview
This lecture provides a complete summary of key concepts, formulas, and practical tips for AQA GCSE Physics Paper 1, covering energy, electricity, particles, and atomic structure.
Energy
- Energy is a conserved quantity that cannot be created or destroyed (except for mass-energy conversion in nuclear reactions).
- Types of energy stores: kinetic, gravitational potential (GPE), elastic potential, thermal, and chemical.
- Kinetic energy: ( E = \frac{1}{2}mv^2 )
- Gravitational potential energy: ( E = mgh ) (use change in height)
- Elastic potential energy: ( E = \frac{1}{2}ke^2 )
- Thermal energy change: ( \Delta E = mc\Delta T ) (specific heat capacity)
- Energy transfer in a closed system is conserved; losses mean the system is not closed.
- Power: ( P = \frac{E}{t} ), unit: watt (W), equivalent to joule/second.
- Efficiency = useful energy out / total energy in (as ratio or %).
Energy Sources & Insulation
- Non-renewable sources: fossil fuels, nuclear fuel.
- Renewable sources: wind, hydroelectric, solar, geothermal, biofuel.
- Energy can be lost from buildings due to poor insulation.
Electricity
- Electricity: flow of charge (usually electrons); measured in coulombs (C).
- Potential difference (PD or voltage): energy transferred per coulomb (( V = \frac{E}{Q} ))
- Current (( I )): rate of flow of charge (( I = \frac{Q}{t} )), measured in amps (A).
- Resistance (( R )): opposes current (( V = IR )), measured in ohms (Ω).
- Ohmic conductors (resistors) have constant resistance; metals and bulbs do not.
- Diode allows current in one direction only; LED emits light.
- Thermistors (resistance falls with temperature) and LDRs (resistance falls with light) are useful for sensors.
Circuits & Power
- Series circuits: PD shared, current same, total resistance sums.
- Parallel circuits: PD same, current shared, total resistance decreases as more branches are added.
- Electrical power: ( P = VI ), alternative: ( P = I^2R ) or ( P = \frac{V^2}{R} ).
- Mains electricity is AC (230V, 50Hz), with live, neutral, and earth wires; fuses prevent excessive current.
Particles & Matter
- Density (( \rho )): mass per unit volume (( \rho = \frac{m}{V} )), units: kg/m³.
- States of matter: solid (fixed positions), liquid (move freely), gas (far apart, compressible).
- Heating increases kinetic energy (temperature rises); during change of state, energy increases potential energy.
- Internal energy = total kinetic + potential energy of particles.
- Specific latent heat (SLH): energy for 1kg change of state (( E = mL )).
- Pressure in gases increases with temperature or when compressed; pressure × volume = constant at constant T.
Atomic Structure & Radioactivity
- Atoms have protons (positive), neutrons (neutral), electrons (negative).
- Atomic number = protons; mass number = protons + neutrons; isotopes have different neutrons.
- Radiation: alpha (2p, 2n), beta (fast electron), gamma (EM wave).
- Alpha: high ionizing, low penetration (stopped by paper); beta: medium both (stopped by Al); gamma: low ionizing, high penetration (reduced by lead/concrete).
- Radioactivity/activity = decay rate, measured in becquerels (Bq).
- Half-life = time for activity (or nuclei/mass) to halve; use graphs to determine.
Nuclear Reactions (Triple Only)
- Nuclear fission: heavy nucleus splits, releases energy and more neutrons (chain reaction).
- Nuclear fusion: light nuclei combine to form heavier nucleus, releases energy.
- Mass can convert to energy in nuclear reactions (mass-energy equivalence).
Key Terms & Definitions
- Energy store — a way energy is held (kinetic, GPE, chemical, etc.).
- Power — rate of energy transfer (W, joule/second).
- Potential difference (PD) — energy per coulomb (V).
- Current (I) — flow of charge per second (A).
- Resistance (R) — how much a component restricts current (Ω).
- Density (ρ) — mass per unit volume (kg/m³).
- Internal energy — sum of kinetic and potential energy in a system.
- Specific heat capacity (SHC) — energy needed to raise 1kg by 1°C.
- Specific latent heat (SLH) — energy for 1kg to change state.
- Half-life — time for half of radioactive nuclei/activity to decay.
- Isotope — atoms of the same element with different neutron numbers.
Action Items / Next Steps
- Review all equations and memorize units.
- Practice rearranging and applying key formulas (especially energy and electricity).
- Perform and understand specific heat capacity and resistance practicals.
- For triple: review nuclear fission, fusion, and mass-energy conversion in detail.