This is a complete revision guide for AQA Combined Science Trilogy Physics Paper 1, covering all four topics in the specification: Energy, Electricity, Particle Model of Matter and Atomic Structure. It is written specifically for the Combined Science course. Content that is Higher Tier only is clearly labelled throughout so Foundation students know exactly what they do not need to revise.
Do not read this passively. For each section, read the explanation, cover the page and try to recall the key points 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. Revisit any section where your recall is weak before moving on.
Topic 4.1: Energy
Energy stores and transfers
A system is an object or group of objects being studied. Energy cannot be created or destroyed — it can only be transferred between stores. This is conservation of energy.
The eight energy stores are: kinetic, thermal, gravitational potential, elastic potential, chemical, magnetic, electrostatic and nuclear. Energy can be transferred by heating, radiation, electrical work or mechanical work.
Examples of energy transfers
- Object projected upwards: kinetic energy store decreases, gravitational potential energy store increases
- Moving object hitting an obstacle: kinetic energy decreases, thermal energy and sound increase
- Vehicle slowing down: kinetic energy decreases, thermal energy of brakes increases
- Electric kettle boiling water: electrical energy transfers to the thermal energy store of the water
Key equations
Kinetic energy: Ek = 1/2 mv squared. Speed is squared, so doubling speed quadruples kinetic energy.
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.
Gravitational potential energy: Ep = mgh, where g is gravitational field strength (9.8 N/kg on Earth).
Specific heat capacity: change in E = mc change in theta. Specific heat capacity is the energy needed to raise the temperature of 1 kg of a substance by 1 degree Celsius. Materials with a high specific heat capacity heat up slowly and store a large amount of energy.
Power: P = E/t or P = W/t. A more powerful appliance transfers energy faster.
Efficiency: useful output energy divided by total input energy. Can also be written using power values. Expressed as a decimal or percentage.
Energy is always conserved. It is dissipated into the thermal store of the surroundings and becomes less useful. In an exam, always say energy is "dissipated" or "transferred to the thermal store of the surroundings" — not lost.
Required practical: specific heat capacity
Aim: determine the specific heat capacity of one or more materials.
- Measure the mass of the block
- Insert a heater and thermometer into the block
- Record the starting temperature
- Heat the block for a known time and record the final temperature
- Calculate energy supplied using E = Pt
- Use the specific heat capacity equation to calculate c
Independent variable: heating time or material. Dependent variable: temperature rise. Control variables: mass, starting temperature, power supplied. Common sources of error include heat loss to the surroundings and inaccurate thermometer readings. Adding insulation and repeating to calculate a mean both improve reliability.
Reducing unwanted energy transfers
Lubrication reduces friction. Insulation reduces heat transfer. Streamlining reduces air resistance. In buildings, thick walls, loft insulation, double glazing and cavity wall insulation all reduce energy loss by reducing thermal conductivity.
Energy resources
Renewable resources include wind, solar, hydroelectric, geothermal, tidal, biofuel and waves. Non-renewable resources include coal, oil, gas and nuclear fuel. Fossil fuels are reliable and have a large energy output but produce greenhouse gases and will eventually run out. Nuclear fuel produces no greenhouse gases during operation but generates radioactive waste. Wind and solar are renewable with no fuel cost but are weather-dependent and unreliable.
Topic 4.2: Electricity
Circuit symbols
You need to be able to draw and interpret circuit diagrams using standard symbols for: cell, battery, lamp, resistor, variable resistor, diode, LED, thermistor, LDR, ammeter, voltmeter, fuse, switch and motor. The ammeter is always connected in series. The voltmeter is always connected in parallel.
Current, charge and potential difference
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. In a series circuit, current is the same everywhere.
Potential difference (voltage) is the energy transferred per unit charge. The equation linking current, resistance and potential difference is V = IR. Higher resistance means lower current 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
- Ohmic conductor: current directly proportional to voltage, straight line graph through the origin, resistance stays constant
- Filament lamp: resistance increases as temperature increases, curved graph
- Diode: current flows in one direction only, high resistance in the reverse direction
- Thermistor: resistance decreases as temperature increases, used in thermostats and temperature sensors
- LDR: resistance decreases as light intensity increases, used in automatic lights and burglar alarms
Required practical: I-V characteristics
Students investigate the I-V characteristics of a resistor, filament lamp and diode. Set up the circuit, vary the potential difference and measure the current. Plot current against voltage. Expected results: resistor gives a straight line, filament lamp gives a curve, diode shows current only above a threshold voltage.
Series and parallel circuits
In series circuits, current is the same throughout, voltage is shared between components and total resistance adds up: Rtotal = R1 + R2.
In parallel circuits, voltage is the same across all branches, current splits between branches and total resistance decreases as more branches are added.
Mains electricity
Direct current flows in one direction only. Alternating current constantly changes direction. UK mains electricity is alternating current at 230 V and 50 Hz.
In a three-core cable: the live wire is brown and is dangerous even when the switch is open; the neutral wire is blue and completes the circuit; the earth wire is green and yellow and is a safety wire that prevents an appliance becoming live 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.
The National Grid
The National Grid transfers electricity across the country. Step-up transformers increase voltage and reduce current, which reduces energy loss in the transmission cables. Step-down transformers reduce voltage to a safe level for homes.
Higher Tier only: for transformers, Vp multiplied by Ip = Vs multiplied by Is, where p is primary and s is secondary.
Current is the flow of charge, measured in amperes. Voltage (potential difference) is the energy transferred per unit charge, measured in volts. Confusing these two in exam answers is one of the most common errors across Physics Paper 1.
Topic 4.3: Particle Model of Matter
Density
Density is mass per unit volume. The equation is: density = m/V, where density is in kg per cubic metre, mass is in kg and volume is in cubic metres. Solids have the highest density because particles are tightly packed. Liquids have medium density. Gases have the lowest density because particles are far apart.
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.
Changes of state
Changes of state are physical changes. Mass is conserved and no new substance is formed. The processes are: melting (solid to liquid), freezing (liquid to solid), boiling (liquid to gas), condensing (gas to liquid) and sublimation (solid directly to gas or vice versa). Particles are rearranged during these changes, not chemically altered.
Internal energy and specific heat capacity
Internal energy is the total kinetic energy and potential energy of all the particles in a system. Heating a substance increases its internal energy, which either raises its temperature or causes a change of state — not both at the same time.
Specific heat capacity equation: change in E = mc change in theta. High specific heat capacity materials heat up slowly and store large amounts of energy. Water has a particularly high specific heat capacity, which is why it is used as a coolant.
Specific latent heat and heating graphs
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. Latent heat of fusion applies to the solid-to-liquid change. Latent heat of vaporisation applies to the liquid-to-gas change. Energy during a change of state breaks bonds between particles rather than increasing kinetic energy, which is why temperature stays constant.
On a heating graph, a sloping section means temperature is rising. A flat section means a change of state is occurring and temperature stays constant despite energy still being transferred.
Gas pressure and particle motion
Gas particles move randomly and constantly collide with the walls of their container. Pressure is caused by these collisions. When temperature increases, particles move faster, collisions increase in frequency and force, and pressure increases if volume is fixed.
This is one of the most tested points in this topic. On a heating graph, flat sections are not errors. Energy is still being transferred but it is breaking bonds between particles rather than raising temperature. Never say the temperature "should be rising" during these sections.
Topic 4.4: Atomic Structure
Structure of the atom
Atoms are very small, approximately 1 x 10 to the power of negative 10 metres in diameter. The nucleus contains protons and neutrons and is tiny but accounts for most of the atom's mass. Electrons occupy energy levels around the nucleus. Atoms are mostly empty space.
Atomic number is the number of protons. Mass number is the total number of protons and neutrons. In a neutral atom, the number of electrons equals the number of protons. Ions are atoms that have gained or lost electrons — losing electrons produces a positive ion.
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 gold foil experiment showed that most alpha particles passed straight through, leading to the conclusion that the atom is mostly empty space with a small dense positive nucleus. Bohr placed electrons in fixed energy levels or shells. Chadwick discovered the neutron, completing the nuclear model. Scientific models change when new evidence appears.
Radioactive decay
Radioactive decay is a random process where unstable nuclei emit radiation to become more stable. Activity is the number of decays per second, measured in becquerels.
- Alpha radiation: 2 protons and 2 neutrons, highly ionising, low penetration, stopped by paper or a few centimetres of air
- Beta radiation: a fast-moving electron, medium ionising power, medium penetration, stopped by a few millimetres of aluminium
- Gamma radiation: electromagnetic wave, weakly ionising, highly penetrating, significantly reduced only by thick lead or concrete
Nuclear equations
Mass number and atomic number are both conserved in nuclear equations. In alpha decay, mass number decreases by 4 and atomic number decreases by 2. In beta decay, mass number is unchanged and atomic number increases by 1. In gamma emission, neither value changes.
Half-life
Half-life is the time taken for the activity or count rate of a radioactive sample to halve, or for the number of unstable nuclei to halve. Decay is random so half-life is a statistical measure. Different isotopes have different half-lives.
Higher Tier only: you may be asked to calculate remaining activity after multiple half-lives. After one half-life, 50% of the original activity remains. After two half-lives, 25%. After three, 12.5%, and so on.
Contamination and irradiation
Contamination is when radioactive material gets onto or inside an object or person. The object itself becomes a source of radiation. Irradiation is when an object is exposed to radiation from an external source. An irradiated object does not become radioactive. Contamination is generally more dangerous because the source remains in contact with the person.
This distinction between contamination and irradiation is tested directly. Contamination means the radioactive material is on or in the object, making the object itself a source. Irradiation means exposure from an outside source with no lasting effect on the object itself.
Quick reference: all equations for Paper 1
- Kinetic energy: Ek = 1/2 mv squared
- Elastic potential energy: Ee = 1/2 ke squared
- Gravitational potential energy: Ep = mgh
- 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
- Electrical power: P = VI and P = I squared multiplied by R
- Energy transfer: E = Pt and E = QV
- Density: density = m/V
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
- Forgetting that speed is squared in the kinetic energy equation
- Mixing up contamination and irradiation
- Saying atoms are solid rather than mostly empty space
- Forgetting that temperature stays constant during changes of state
- Not showing working in multi-step calculations
If you are sitting triple science rather than combined, our separate Physics Paper 1 guide covers the same topics with the additional content required for that specification. For exam technique and command word guidance, read our post on the biggest mistakes GCSE Science students make in exams.
