Overview
This lecture covers all key content for AQA GCSE Physics Paper 1, including core principles, formulas, and practicals for Energy, Electricity, Particle Model of Matter, and Atomic Structure/Nuclear Physics.
Energy Stores and Transfers
- Energy is a conserved quantity that cannot be created or destroyed.
- Main energy stores: kinetic, gravitational potential (GPE), elastic potential, thermal, and chemical.
- Kinetic energy: E = ½mv².
- Gravitational potential energy: E = mgh.
- Elastic potential energy: E = ½ke².
- Change in thermal energy: E = mcΔT, where c is specific heat capacity.
- Energy is measured in joules (J); all stores can transform, but total energy remains constant in a closed system.
Energy Calculations & Efficiency
- In closed systems, GPE lost = kinetic energy gained when falling.
- Rearranging equations (e.g., for velocity): v = √(2E/m).
- Work means energy transferred.
- Specific heat capacity: measured by heating a known mass and recording temperature change.
- Power measures energy transfer per second: P = E/t.
- Efficiency: useful energy out / total energy in (expressed as decimal or percentage).
Energy Resources
- Non-renewable: fossil fuels, nuclear fuel (finite).
- Renewable: wind, hydroelectric, solar, geothermal, biofuel.
Electricity Basics and Circuits
- Electricity is the flow of charge (usually electrons) through a circuit.
- Potential difference (PD)/voltage is energy per coulomb (V = E/Q).
- Current is rate of charge flow (I = Q/t); measured in amps.
- Resistance opposes current (Ohm's Law: V = IR).
- Ohmic conductors have constant resistance; metals and bulbs show increasing resistance with current.
- Diodes allow current in one direction only.
- Series circuits: total PD shared, current same everywhere, resistance adds.
- Parallel circuits: PD same across branches, current splits, total resistance decreases.
Components & Practical Circuits
- Thermistors: resistance decreases as temperature increases.
- Light-Dependent Resistors (LDR): resistance decreases as light intensity increases.
- Power in electrical circuits: P = IV or P = I²R.
- Direct current (DC) flows one way (from batteries); alternating current (AC) periodically reverses (mains electricity is AC, 230 V, 50 Hz).
- Wire colors: live (brown), neutral (blue), earth (yellow/green); earth wire is for safety.
- Fuses protect circuits by breaking if current exceeds rating.
National Grid & Transmission
- High voltage, low current transmission reduces energy loss (P = I²R).
- Transformers step up/down voltage for efficient transmission and safer use.
Static Electricity & Electric Fields (Triple Only)
- Friction can transfer electrons, creating positive/negative objects.
- Like charges repel, opposite charges attract; fields are strongest close to charges.
Particle Model of Matter
- Density: ρ = m/V, measured in kg/m³.
- Solids, liquids, and gases differ in particle arrangement and movement.
- To find density of irregular objects, use water displacement.
- State changes (melting, boiling) involve energy without temperature change (potential energy increases).
- Internal energy = total kinetic + potential energy of particles.
Heating, Cooling & Gases
- Specific latent heat (SLH): energy to change state without temperature change (E = mL).
- For gases: heating increases pressure; pV = constant at constant temperature (Boyle’s Law).
Atomic Structure and Nuclear Physics
- Key models: Plum pudding, nuclear model, shell model, discovery of neutrons.
- Atomic number = number of protons; mass number = protons + neutrons.
- Isotopes: same protons, different neutrons.
- Types of radiation: alpha (helium nucleus), beta (fast electron), gamma (EM wave).
- Alpha radiation: highly ionizing, blocked by paper.
- Beta: moderate ionizing, blocked by aluminum.
- Gamma: low ionizing, very penetrating, reduced by lead/concrete.
- Half-life: time for activity or nuclei to halve.
- Radioactivity measured in becquerels (Bq) using a GM tube.
Nuclear Reactions (Triple Only)
- Nuclear fission: heavy nucleus splits, releasing energy and more neutrons (chain reaction).
- Nuclear fusion: light nuclei fuse, releasing energy (occurs in the Sun).
- Mass converts to energy in nuclear reactions (E=mc² principle).
Key Terms & Definitions
- Specific Heat Capacity (SHC) — Energy needed to raise 1 kg by 1°C.
- Specific Latent Heat (SLH) — Energy needed to change state of 1 kg with no temperature change.
- Potential Difference (PD) — Energy transferred per coulomb of charge.
- Current (I) — Rate of flow of electric charge.
- Resistance (R) — Opposition to current, measured in ohms.
- Isotope — Same element with different numbers of neutrons.
- Half-life — Time for half the radioactive nuclei or activity to decay.
Action Items / Next Steps
- Practice rearranging and applying physics equations.
- Review required practicals (SHC, resistance, density).
- Memorize key definitions and SI units.
- Complete any assigned homework or additional reading on nuclear physics if taking triple science.