AQA GCSE Physics: Electricity, Magnetism and Electromagnetism Revision Guide

Electricity and Magnetism are two of the most heavily tested topics on the AQA GCSE Physics specification. Between them, they span a huge range of content -- from the basic behaviour of charge in a circuit right through to the operation of transformers and the National Grid. They appear on Paper 1 and Paper 2 respectively, so you will encounter questions on these topics in both exams.

What makes these topics rewarding is that they are deeply interconnected. Understanding how current flows through circuits sets you up for understanding how electromagnets work. Understanding the motor effect leads directly into generators and induced potential. This guide covers everything you need to know about Electricity (Topic 2) and Magnetism and Electromagnetism (Topic 7) on the AQA specification.

Part 1: Electricity

Electricity is one of the largest and most calculation-heavy topics on the specification. It appears on Paper 1 and typically accounts for a significant share of the marks. You need to be confident with definitions, circuit rules, equations, and graph interpretation.

Circuit Symbols and Components

You are expected to recognise and use the standard circuit symbols for: cell, battery, switch (open and closed), lamp, resistor, variable resistor, ammeter, voltmeter, diode, LED, thermistor, LDR, fuse, and motor. These symbols appear in circuit diagrams throughout the exam, and you need to be able to both read and draw circuits using them.

A cell provides a potential difference from a chemical reaction. A battery is two or more cells connected together. An ammeter measures current and must be connected in series. A voltmeter measures potential difference and must be connected in parallel across the component being measured.

Current, Charge, and Potential Difference

Current is the rate of flow of electrical charge, measured in amperes (A). Charge is measured in coulombs (C), and the relationship is:

Q = I x t

This equation must be memorised -- it is not provided on the equation sheet. Potential difference (often called voltage) is the energy transferred per unit of charge passing between two points in a circuit, measured in volts (V). One volt means one joule of energy transferred per coulomb of charge. The defining equation is:

E = Q x V

Where E is energy in joules, Q is charge in coulombs, and V is potential difference in volts.

Resistance and Ohm's Law

Resistance is the opposition to the flow of current, measured in ohms (the symbol for which is the Greek letter omega). The greater the resistance of a component, the smaller the current that flows for a given potential difference. Ohm's law gives the relationship:

V = I x R

This is one of the most important equations in GCSE Physics and must be memorised. You should be confident rearranging it to find any of the three quantities: R = V / I and I = V / R. An ohmic conductor (such as a resistor at constant temperature) has a constant resistance -- current is directly proportional to potential difference, giving a straight-line I-V graph through the origin.

You need to know the I-V graphs for three components. A fixed resistor gives a straight line through the origin. A filament lamp curves as the filament heats up and resistance increases. A diode allows current in one direction only, showing a sharp rise after a threshold voltage and no current in reverse.

Thermistors decrease in resistance as temperature increases. LDRs decrease in resistance as light intensity increases. Both are used in sensing circuits.

Series and Parallel Circuits

Understanding the rules for series and parallel circuits is essential. These are tested frequently in both calculations and longer-answer explanations.

Series circuits:

• There is only one path for current to flow
• The current is the same through every component
• The total potential difference of the supply is shared between components
• The total resistance is the sum of individual resistances: R_total = R1 + R2 + R3...

Parallel circuits:

• There are multiple paths for current to flow
• The potential difference across each branch is the same (equal to the supply voltage)
• The total current from the supply is the sum of the currents through each branch
• Adding more resistors in parallel decreases the total resistance

The behaviour of parallel circuits can seem counterintuitive. Adding another resistor in parallel provides an additional path for current, so more current flows from the supply overall even though each branch independently obeys Ohm's law. The total resistance of a parallel combination is always less than the smallest individual resistance.

Mains Electricity

The UK mains supply provides alternating current (ac) at approximately 230 V and 50 Hz -- unlike the direct current (dc) from cells and batteries.

The three-pin plug uses three wires:

• Live wire (brown) -- carries the alternating potential difference, alternating between roughly +325 V and -325 V
• Neutral wire (blue) -- completes the circuit at approximately 0 V
• Earth wire (green and yellow) -- a safety wire at 0 V providing a low-resistance path to earth during faults

A fuse melts and breaks the circuit if current is too high, and is always in the live wire. A circuit breaker does the same job but can be reset. The live wire is dangerous even when a switch is open, because it still carries 230 V relative to earth.

Electrical Power and Energy

Power is the rate of energy transfer, measured in watts. Two key equations:

P = I x V

P = I squared x R

Both must be memorised. The second follows from substituting V = IR into the first and is useful when you know current and resistance but not voltage.

Energy transferred depends on power and time:

E = P x t

In domestic contexts, energy is measured in kilowatt-hours (kWh). One kilowatt-hour is the energy transferred by a 1 kW device running for 1 hour. Cost is calculated as power (kW) multiplied by time (hours) multiplied by the price per kWh.

The National Grid

The National Grid distributes electrical energy from power stations to consumers using cables and transformers. It operates at very high voltages -- typically 275,000 V or 400,000 V.

High voltage reduces energy losses during transmission. The power lost as heat in the cables is P = I squared x R. A step-up transformer increases voltage, which reduces current for the same power (since P = IV). Lower current means much less energy wasted as heat. At the consumer end, a step-down transformer reduces voltage to 230 V for domestic use.

Part 2: Magnetism and Electromagnetism

Magnetic Fields and Poles

A magnet has a north and south pole. Like poles repel; unlike poles attract. The magnetic field is the region where a force acts on magnetic materials. Field lines run from north to south outside the magnet -- closer lines indicate a stronger field, and they never cross.

A permanent magnet produces its own field at all times. An induced magnet is a material that becomes magnetic only when placed inside a magnetic field. Induced magnets are always attracted to the permanent magnet that induced them. When removed from the field, an induced magnet quickly loses most or all of its magnetism. Magnetic materials include iron, steel, nickel, and cobalt. The Earth's magnetic field can be modelled as a bar magnet, with a compass needle aligning with the field to indicate direction.

Electromagnets

When an electric current flows through a wire, it produces a magnetic field around the wire. The field lines form concentric circles centred on the wire. The direction of the field can be determined using the right-hand grip rule: grip the wire with your right hand so that your thumb points in the direction of conventional current, and your fingers curl in the direction of the magnetic field.

A solenoid is a coil of wire that produces a field pattern similar to a bar magnet, with a north pole at one end and a south pole at the other. Inside the solenoid, the field is strong and approximately uniform. An electromagnet is a solenoid with a soft iron core, which greatly increases field strength. Electromagnets are useful because they can be switched on and off. Their strength increases with more current, more turns on the coil, or the addition of a soft iron core.

The Motor Effect and Fleming's Left-Hand Rule

A current-carrying conductor in a magnetic field experiences a force -- the motor effect. The force is maximum when the wire is perpendicular to the field. Its magnitude is given by:

F = B x I x l

Where B is magnetic flux density in tesla, I is current in amperes, and l is the length of conductor in the field in metres. This equation is on the equation sheet.

Fleming's left-hand rule determines the direction of the force. Hold your left hand with thumb, first finger, and second finger at right angles:

• First finger -- direction of the magnetic Field (north to south)
• Second finger -- direction of conventional Current (positive to negative)
• Thumb -- direction of the Force (motion)

Electric Motors

A dc motor has a coil on an axle within a magnetic field. Current through the coil creates forces in opposite directions on each side (via the motor effect), producing rotation. A split-ring commutator reverses the current direction every half turn so the coil spins continuously rather than oscillating. Motor speed increases with stronger current, a stronger magnet, or more turns on the coil.

Loudspeakers

A loudspeaker converts electrical signals into sound using the motor effect. A voice coil sits inside a permanent magnet's field. Alternating current makes the coil move back and forth, vibrating an attached paper cone that creates sound waves. The frequency of vibration matches the signal frequency (determining pitch), and the amplitude determines loudness.

The Generator Effect and Induced Potential (Higher Tier)

The generator effect is the reverse of the motor effect. Moving a conductor through a magnetic field -- or changing the field around a conductor -- induces a potential difference. If the conductor is in a complete circuit, a current flows. This is electromagnetic induction.

The induced potential difference increases with faster movement, a stronger magnet, or more turns on the coil. Reversing the direction of movement reverses the induced potential difference.

An alternator uses a rotating coil in a magnetic field with slip rings and brushes to produce alternating current. A dynamo uses a split-ring commutator instead, producing direct current.

Transformers (Higher Tier)

A transformer changes the voltage of an ac supply using two coils -- primary and secondary -- wound around a shared iron core. Alternating current in the primary creates a changing magnetic field that induces an alternating voltage in the secondary.

The transformer equation is:

Vp / Vs = np / ns

A step-up transformer has more secondary turns than primary, increasing voltage. A step-down transformer has fewer secondary turns, decreasing voltage.

If a transformer is assumed to be 100% efficient (a common assumption at GCSE level), the power input equals the power output:

Vp x Ip = Vs x Is

This means that if voltage is stepped up, current is stepped down, and vice versa. This principle is fundamental to how the National Grid operates -- stepping voltage up for efficient long-distance transmission and stepping it back down for safe domestic use. In reality, some energy is lost as heat in the coils and core, but well-designed transformers can achieve efficiencies above 99%.

Key Equations Summary

Equations marked with an asterisk must be memorised:

Electricity:

• *Q = I x t
• *V = I x R
• *P = I x V
• *P = I squared x R
• *E = Q x V
• E = P x t

Magnetism:

• F = B x I x l
• Vp / Vs = np / ns (Higher)
• Vp x Ip = Vs x Is (Higher)

Exam Technique

Show your working. Write the equation, substitute values, and show each step. You earn marks for method even if the final answer is wrong.

Learn the circuit rules precisely. A common error is saying current is shared in series or voltage is the same in series -- both are incorrect.

Use Fleming's left-hand rule physically. Hold up your left hand in the exam rather than trying to visualise it. It is much more reliable.

Structure six-mark answers logically. For a motor question, explain in sequence: current flows, the coil is in a field, the motor effect produces a force, the commutator reverses current every half turn, and the coil rotates continuously.

Convert units before substituting. Time in minutes or hours must become seconds; power in kilowatts must become watts. Converting first prevents avoidable errors.

Prepare with LearningBro

These two topics cover a huge amount of content, from fundamental circuit theory to electromagnetic induction. The best way to consolidate your understanding is through active recall -- testing yourself repeatedly on the key concepts, equations, and applications.

LearningBro offers targeted assessment courses that break these topics down into focused question sets, helping you identify gaps and build exam confidence.

• AQA GCSE Physics: Electricity
• AQA GCSE Physics: Magnetism and Electromagnetism

Work through the questions, review the explanations, and revisit any areas where you are not yet confident. Consistent, active practice is the most effective way to turn knowledge into marks.