AQA GCSE Physics 4.2 Electricity: a complete overview of current, circuits, mains, power and static electricity

What topic 4.2 actually demands

Electricity is one of the most equation-heavy topics in AQA GCSE Physics, and it rewards confident circuit reasoning. Examiners test precise definitions, the ability to apply circuit rules, fluent calculation with the power and energy equations, and clear explanations of mains safety and the national grid.

This guide walks through all five dot points of the topic, then sets out the exam patterns AQA repeats. Each dot point has a matching page with practice questions; this overview ties them together.

Current, potential difference and resistance

Current is the rate of flow of charge, $Q = It$, measured by an ammeter in series. Potential difference is the energy transferred per unit charge, measured by a voltmeter in parallel. Resistance opposes current, and Ohm's law is $V = IR$.

The I-V characteristics are a favourite: an ohmic resistor gives a straight line through the origin (constant resistance), a filament lamp gives an S-shaped curve because its resistance rises as it heats, and a diode conducts in one direction only.

Series and parallel circuits

In series, current is the same everywhere, potential differences add to the supply, and resistances add. In parallel, every branch has the full supply potential difference, branch currents add, and the total resistance is less than the smallest resistor. Adding resistors in series increases total resistance; adding them in parallel decreases it by providing extra paths.

Domestic electricity and mains

Direct current flows one way (from a cell); alternating current reverses repeatedly. The UK mains is a.c. at about $230\,V$ and $50\,Hz$. The three-core cable has a brown live wire (carries about $230\,V$), a blue neutral wire (near $0\,V$) and a green-and-yellow earth wire (a safety wire that carries current only in a fault).

Electrical power and the national grid

Electrical power is $P = VI$ or $P = I^2R$; energy is $E = Pt$ or $E = QV$. The national grid uses step-up transformers to transmit at high voltage and low current, cutting the $I^2R$ losses, then step-down transformers to lower the voltage for safe domestic use.

Static electricity

Rubbing two insulators transfers electrons: one becomes negative, the other positive. Like charges repel, opposite charges attract, a non-contact force. Large charge build-up can cause a spark, and a charged object is surrounded by an electric field that is strongest close to it.

How topic 4.2 is examined

A typical AQA profile for Electricity:

• Short answer. Defining current, potential difference and resistance; stating series and parallel rules; recalling mains values and wire colours.
• Calculations. Charge, Ohm's law, power and energy, often combined within multi-step circuit questions.
• Graph work. Sketching and interpreting the I-V characteristics of resistors, lamps and diodes.
• Extended answers. Explaining mains safety (live wire, earth wire and fuse) and why the national grid uses transformers.

Check your knowledge

A mix of recall and calculation questions covering topic 4.2. Attempt them under timed conditions, then check against the solutions.

1. Define electric current and state how it is measured. (2 marks)
2. State Ohm's law as an equation. (1 mark)
3. A $3\,A$ current flows for $20\,s$. Calculate the charge transferred. (2 marks)
4. Two $5\,\Omega$ resistors are in series across a $20\,V$ supply. Calculate the current. (3 marks)
5. State the potential difference and frequency of the UK mains supply. (2 marks)
6. A $1500\,W$ appliance runs for $2$ minutes. Calculate the energy transferred. (3 marks)
7. Explain why the national grid transmits at high voltage and low current. (2 marks)
8. Explain how a plastic rod becomes positively charged when rubbed. (2 marks)