This is a complete revision guide for AQA GCSE Physics Paper 1, covering all four topics in the specification: Energy, Electricity, Particle Model of Matter and Atomic Structure. It includes every equation, definition, required practical and key explanation you need before sitting the paper. Sections marked HT are Higher Tier content only.
Do not read this passively. For each section, read the explanation, cover the page and try to recall it from memory. Then practise calculations. The students who improve fastest are the ones who test themselves repeatedly rather than rereading notes.
Work through each topic section by section. After reading, close the page and try to recall the key points and equations from memory. Use this as a prompt for active recall, not a substitute for it.
Topic 4.1: Energy
Energy stores
A system is an object or group of objects being studied. When a system changes, energy is transferred between stores. Energy cannot be created or destroyed — this is conservation of energy.
The eight energy stores are: kinetic, thermal (internal), gravitational potential, elastic potential, chemical, magnetic, electrostatic and nuclear.
- Kinetic: stored by moving objects
- Thermal: stored by particles inside an object due to their movement and arrangement
- Gravitational potential: stored by objects raised in a gravitational field
- Elastic potential: stored when objects are stretched or compressed
- Chemical: stored in fuels, food and batteries
- Nuclear: stored inside atomic nuclei
Energy transfer pathways
Energy can be transferred mechanically (forces doing work), electrically (charge flowing), by heating (temperature differences) or by radiation (waves such as light or infrared).
When a ball is thrown upwards, kinetic energy decreases and gravitational potential energy increases. At the top, gravitational potential energy is maximum and kinetic energy is minimum. As it falls, the process reverses. Some energy is dissipated by air resistance throughout.
When brakes are applied to a vehicle, friction acts and kinetic energy transfers into thermal energy of the brakes and surroundings. In an electric kettle, energy transfers electrically from the mains to the heating element, then by heating into the water.
Key equations
Kinetic energy: Ek = 1/2 mv squared, where Ek is in joules, m is mass in kg and v is speed in m/s. Speed is squared, so doubling speed quadruples kinetic energy.
Gravitational potential energy: Ep = mgh, where m is mass in kg, g is gravitational field strength (9.8 N/kg on Earth) and h is height in metres.
Elastic potential energy: Ee = 1/2 ke squared, where k is the spring constant and e is the extension. This equation only applies before the limit of proportionality is exceeded.
Specific heat capacity: change in E = mc change in theta, where m is mass, c is specific heat capacity and the change in theta is the temperature change. Specific heat capacity is the energy required to raise the temperature of 1 kg of a substance by 1 degree Celsius.
Power: P = E/t or P = W/t, where power is in watts, energy in joules and time in seconds. One watt equals one joule per second.
Efficiency: efficiency = useful output energy divided by total input energy. Can be expressed as a decimal or percentage.
Energy is always conserved. It is dissipated into the thermal stores of the surroundings and becomes less useful. Saying energy is "lost" in an exam answer will not score marks. Say it is "dissipated" or "transferred to the thermal store of the surroundings."
Required practical: specific heat capacity
Students heat a material using an electric heater, measure the temperature increase over time and calculate the energy supplied using E = Pt. This links electrical energy transfer to thermal energy. Know the variables: independent is the energy supplied, dependent is the temperature change, control variables include the mass of the material and the insulation used.
Energy resources
Renewable resources include wind, solar, hydroelectric, tidal, geothermal and biofuel. Non-renewable resources include coal, oil, gas and nuclear fuel. Renewable resources are replenished naturally and do not run out. Non-renewable resources will eventually be depleted. Fossil fuels are reliable but produce greenhouse gases contributing to climate change. Wind and solar are renewable but less reliable because they depend on weather conditions.
Topic 4.2: Electricity
Current, charge and potential difference
Electric current is the rate of flow of charge. The equation is Q = It, where Q is charge in coulombs, I is current in amperes and t is time in seconds.
Potential difference (also called voltage) is the energy transferred per unit charge. The equation linking current, resistance and potential difference is V = IR, where V is potential difference in volts, I is current in amperes and R is resistance in ohms. If resistance increases, current decreases for a given voltage.
Required practical: resistance
Students investigate factors affecting resistance including the length of wire and resistors in series and parallel. Build a circuit with an ammeter and voltmeter, measure current and potential difference, calculate resistance using V = IR, then change the wire length and repeat. A longer wire has greater resistance because electrons collide more often as they travel through it.
Components and their characteristics
An ohmic conductor obeys Ohm's Law. At constant temperature, current is directly proportional to potential difference and resistance stays constant. A straight line through the origin on a current-voltage graph indicates an ohmic conductor.
A filament lamp has increasing resistance as temperature increases because vibrating ions make electron flow harder. Its current-voltage graph is a curve, not a straight line.
A diode only allows current to flow in one direction. In the reverse direction, resistance is very high and current is effectively zero.
A thermistor has decreasing resistance as temperature increases. It is used in thermostats and temperature sensors.
An LDR (light-dependent resistor) has decreasing resistance as light intensity increases. It is used in automatic lighting circuits.
Required practical: I-V characteristics
Students investigate current and voltage for a resistor, filament lamp and diode. Plotting current against voltage for each component gives characteristic graphs. A straight line through the origin indicates a linear (ohmic) component. A curve indicates resistance is changing.
Series and parallel circuits
In series circuits, current is the same throughout and voltage is shared between components. Total resistance equals the sum of individual resistances: Rtotal = R1 + R2.
In parallel circuits, voltage is the same across all branches and current splits between branches. Adding more branches reduces total resistance.
Mains electricity
UK mains supply provides alternating current at 230 V and 50 Hz. Alternating current changes direction repeatedly. Direct current flows in one direction only.
In a three-core cable: the live wire is brown and carries the alternating potential difference; the neutral wire is blue and completes the circuit; the earth wire is green and yellow and is a safety wire that carries current only during a fault.
Power and energy in circuits
Power equations: P = VI and P = I squared multiplied by R. Energy transfer equations: E = Pt and E = QV. More powerful devices transfer more energy each second.
The National Grid
The National Grid transfers electricity across the country. Step-up transformers increase voltage and reduce current, which reduces energy loss in transmission cables. Step-down transformers reduce voltage to a safe level for homes and businesses.
Static electricity
When insulating materials are rubbed together, electrons transfer from one material to the other. The material gaining electrons becomes negatively charged. The material losing electrons becomes positively charged. Like charges repel and opposite charges attract. Charged objects create electric fields around themselves. Electric fields explain non-contact forces between charged objects.
Current is the flow of charge measured in amperes. Voltage (potential difference) is the energy transferred per unit charge, measured in volts. These are different quantities and mixing them up in exam answers is one of the most common errors in Physics Paper 1.
Topic 4.3: Particle Model of Matter
Density
Density is mass per unit volume. The equation is: density = mass divided by volume (rho = m/V), where density is in kg per cubic metre, mass is in kg and volume is in cubic metres.
Required practical: density
For a regular solid, measure the dimensions and calculate volume, then measure mass and use the density equation. For an irregular solid, measure mass first, then use a displacement can or measuring cylinder to find volume by water displacement. For a liquid, measure the mass of a known volume. The key skill is choosing the correct method for the shape of the object.
States of matter
Solid particles are closely packed in fixed positions and can only vibrate. Liquid particles are close together but able to move around each other. Gas particles are far apart and move randomly and quickly in all directions.
Changes of state
Changes of state include melting, freezing, boiling, condensing, evaporating and sublimation. These are physical changes — mass is conserved and no new substance is formed. During a change of state, temperature remains constant even though energy is still being transferred. Energy is used to separate particles rather than increase their kinetic energy.
On a heating graph, flat sections indicate changes of state. The temperature only rises when all particles have completed the state change.
Internal energy
Internal energy is the total kinetic and potential energy of all the particles in a system. Heating a substance increases its internal energy. This either increases the temperature of the substance or causes a change of state, but not both at the same time.
Specific latent heat
Specific latent heat is the energy needed to change the state of 1 kg of a substance without changing its temperature. The equation is E = mL, where E is energy in joules, m is mass in kg and L is the specific latent heat in J/kg.
Specific latent heat of fusion applies to the solid-to-liquid change. Specific latent heat of vaporisation applies to the liquid-to-gas change.
Gas pressure
Gas pressure is caused by particles colliding with the walls of the container. Increasing temperature increases the kinetic energy of particles, so they collide more frequently and with more force, increasing pressure.
Pressure-volume relationship (HT)
For a fixed mass of gas at constant temperature, pressure multiplied by volume is constant (pV = constant). If volume decreases, pressure increases proportionally. If volume increases, pressure decreases.
Doing work on a gas increases its internal energy and therefore increases its temperature. A bicycle pump becoming warm when used is an example of this.
This surprises students every year. On a heating graph, the flat sections are not errors. Energy is still being transferred but it is being used to break bonds between particles rather than raise temperature. Do not say the temperature "should be rising" during these sections.
Topic 4.4: Atomic Structure
Structure of the atom
Atoms contain protons, neutrons and electrons. Protons have a positive charge and relative mass 1. Neutrons have no charge and relative mass 1. Electrons have a negative charge and a tiny mass. Most of the mass is concentrated in the nucleus. Atoms are mostly empty space.
Atomic number is the number of protons in the nucleus. Mass number is the total number of protons and neutrons. Atoms are neutral because the number of electrons equals the number of protons.
Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. They have the same atomic number but different mass numbers.
Development of the atomic model
Dalton described atoms as solid spheres. Thomson discovered the electron and proposed the plum pudding model, a positive sphere with electrons embedded throughout. Rutherford's alpha scattering experiment showed that most particles passed straight through a thin gold foil, some deflected slightly and a very small number bounced back, leading to the conclusion that the atom is mostly empty space with a small dense positive nucleus. Bohr refined the model by placing electrons in specific energy levels or shells. Chadwick later discovered the neutron, completing the nuclear model.
Radioactive decay
Some nuclei are unstable and emit radiation to become more stable. This process is random and cannot be predicted for any individual nucleus. Activity is the number of decays per second and is measured in becquerels.
Alpha particles contain 2 protons and 2 neutrons. They are highly ionising, have low penetration and are stopped by a sheet of paper or a few centimetres of air.
Beta particles are fast-moving electrons. They have medium ionising power and medium penetration, stopped by a few millimetres of aluminium.
Gamma rays are electromagnetic waves. They are weakly ionising and highly penetrating, significantly reduced only by thick lead or several metres of concrete.
Nuclear equations
In alpha decay, mass number decreases by 4 and atomic number decreases by 2. In beta decay, atomic number increases by 1 and mass number is unchanged. In gamma decay, neither the mass number nor atomic number changes — gamma emission accompanies other decay types.
Half-life
Half-life is the time taken for the activity to halve, or equivalently for the number of unstable nuclei to halve. Radioactive decay is random so half-life is a statistical measure. After one half-life, 50% of the original nuclei remain. After two half-lives, 25% remain. After three half-lives, 12.5% remain.
A common error is confusing half-life with the time for all nuclei to decay. Half-life only tells you when half the unstable nuclei have decayed. Complete decay takes many multiples of the half-life and in theory the activity never reaches exactly zero.
Contamination and irradiation
Contamination is when radioactive material gets onto or inside an object or person. Irradiation is when an object is exposed to radiation from an external source. Irradiated objects do not become radioactive. Contamination is generally more dangerous because the source remains in contact with the person.
Background radiation
Background radiation is always present in the environment. Sources include rocks (particularly granite), cosmic rays from space, medical sources, nuclear fallout and food. Background radiation must be accounted for in any experiment measuring radioactive decay.
Uses of radiation
- Medical tracers: gamma radiation, because it can pass through the body and be detected externally
- Cancer treatment: gamma radiation directed at tumours
- Sterilising medical equipment: gamma radiation kills bacteria
- Smoke alarms: alpha radiation ionises air between two plates; smoke disrupts this and triggers the alarm
Nuclear fission and fusion
Nuclear fission is the splitting of a large unstable nucleus, such as uranium-235, into two smaller nuclei. It releases energy and produces additional neutrons that can trigger further fissions, creating a chain reaction. Nuclear reactors control this chain reaction to produce electricity. Nuclear weapons use uncontrolled chain reactions.
Nuclear fusion is the joining of two small nuclei to form a larger one, releasing enormous amounts of energy. Fusion powers stars. Extremely high temperatures and pressures are needed to overcome the electrostatic repulsion between nuclei, which is why practical fusion reactors have not yet been achieved at scale.
Quick reference: all equations for Paper 1
- Kinetic energy: Ek = 1/2 mv squared
- Gravitational potential energy: Ep = mgh
- Elastic potential energy: Ee = 1/2 ke squared
- Specific heat capacity: change in E = mc change in theta
- Specific latent heat: E = mL
- Power: P = E/t and P = W/t
- Efficiency: useful output divided by total input
- Charge: Q = It
- Potential difference: V = IR
- Power in circuits: P = VI and P = I squared multiplied by R
- Energy in circuits: E = Pt and E = QV
- Density: density = m/V
- Specific latent heat: E = mL
- Pressure-volume (HT): pV = constant
Most common exam mistakes in Physics Paper 1
- Saying energy is "lost" rather than dissipated into the thermal store of the surroundings
- Forgetting to include units in calculation answers
- Confusing current and voltage in circuit questions
- Forgetting that speed is squared in the kinetic energy equation
- Mixing up contamination and irradiation
- Saying atoms are solid rather than mostly empty space
- Confusing half-life with total decay time
- Forgetting that temperature stays constant during changes of state
- Not showing working in multi-step calculations
- Using the wrong equation for the wrong context
For targeted exam technique advice alongside the content, read our companion post on the biggest mistakes GCSE Science students make in exams, which covers command words and how to structure answers for maximum marks.
