What does the Edexcel Electric circuits module cover?

It covers current as the rate of flow of charge with $I = nAvq$, potential difference and EMF as energy per coulomb, electrical power and energy, resistance and Ohm's law, the I-V characteristics of ohmic conductors, filament lamps and diodes, resistivity and the behaviour of thermistors and LDRs, series and parallel circuits analysed with Kirchhoff's two laws, EMF with internal resistance, and potential dividers used as sensor circuits.

Which equations recur most across Electric circuits?

Current $I = \frac{Q}{t}$ and $I = nAvq$, resistance $R = \frac{V}{I}$, resistivity $R = \frac{\rho L}{A}$, the series and parallel resistor rules, power $P = VI = I^2R = \frac{V^2}{R}$, the potential divider equation $V_{out} = V_{in}\frac{R_2}{R_1 + R_2}$, and the internal-resistance equations $\varepsilon = I(R + r)$ and $V = \varepsilon - Ir$.

Why is the terminal potential difference less than the EMF?

A real cell has internal resistance, so some energy per coulomb is dissipated inside it when it drives a current. These lost volts equal $Ir$, so the terminal potential difference $V = \varepsilon - Ir$ is always less than the EMF whenever current flows, and the drop grows with the current.

What is the most common mistake in this module?

Reading the resistance of a component as the gradient of a curved I-V graph. Resistance is always $\frac{V}{I}$ at the chosen point; only a straight line through the origin has resistance equal to the inverse of the gradient. A close second is adding parallel resistances directly instead of using the reciprocal sum.

How should I revise Electric circuits?

Learn the series and parallel rules cold, then practise applying Kirchhoff's two laws to multi-loop circuits. Match the power equation to whether current or voltage is fixed. Then drill resistivity, potential divider and internal-resistance problems, and rehearse finding EMF and internal resistance from a terminal-pd against current graph.

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Edexcel A-Level Physics Electric circuits: a complete overview of current, resistance, circuits and potential dividers

A deep-dive Edexcel A-Level Physics guide to Electric circuits. Covers current and charge, resistance and resistivity, series and parallel circuits with Kirchhoff's laws and internal resistance, and potential dividers and sensor circuits, with the calculations and exam patterns Edexcel repeats.

Generated by Claude Opus 4.816 min read9PH0Updated 2026-06-02

Reviewed by: AI editorial process; not yet individually human-reviewed

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What this module actually demands
Current, charge and resistance
Circuits, internal resistance and dividers
How this module is examined
Check your knowledge

What this module actually demands

Electric circuits is the circuit-analysis core of Edexcel A-Level Physics. It starts from what current and charge are at the level of moving carriers, builds the idea of resistance and how it depends on material and shape, combines components into series and parallel circuits analysed with Kirchhoff's laws, accounts for the internal resistance of a real cell, and finishes with the potential divider as a practical and sensing tool. The examiners reward clean definitions, the reading of characteristic graphs, and multi-step calculations.

This guide walks through the topics in order and sets out the exam patterns Edexcel repeats. Each topic has a matching dot-point page; this overview ties them together.

Current, charge and resistance

Current and charge defines current as the rate of flow of charge, $I = \frac{Q}{t}$ , links it to carriers through $I = nAvq$ , distinguishes potential difference and EMF as energy per coulomb, and gives the power and energy equations. Resistance and resistivity defines resistance and Ohm's law, interprets the I-V characteristics of ohmic conductors, filament lamps and diodes, uses $R = \frac{\rho L}{A}$ , and describes thermistors and LDRs as sensors.

Circuits, internal resistance and dividers

Circuits and internal resistance gives the series and parallel resistor rules, applies Kirchhoff's two laws (charge conservation at junctions, energy conservation around loops), and accounts for internal resistance through $\varepsilon = I(R + r)$ with terminal pd $V = \varepsilon - Ir$ . Potential dividers uses $V_{out} = V_{in}\frac{R_2}{R_1 + R_2}$ , the potentiometer for a variable output, and a thermistor or LDR to build a sensor circuit.

How this module is examined

A typical Edexcel profile:

Calculations. Drift velocity from $I = nAvq$ , resistivity from wire data, series and parallel combinations, power, potential divider outputs, and current and terminal pd with internal resistance.
Graph and data questions. Reading I-V characteristics, explaining the filament-lamp curve, and finding EMF and internal resistance from a terminal-pd against current graph.
Explanation. Why a metal's resistance rises with temperature, how a thermistor sensor works, and why terminal pd falls as current increases.
Extended answers. Designing a sensor circuit and analysing multi-loop circuits with Kirchhoff's laws.

Check your knowledge

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

Define electric current. (1 mark)
A current of $4.0$ A flows for $30$ s. Find the charge that passes. (1 mark)
A wire of length $1.0$ m and area $4.0 \times 10^{-7}$ m squared has resistivity $1.6 \times 10^{-8}$ ohm m. Find its resistance. (2 marks)
Two $4.0$ ohm resistors are connected in parallel. Find the combined resistance. (2 marks)
A potential divider has a $1.0$ k-ohm and a $4.0$ k-ohm resistor across $10$ V. Find the output across the $4.0$ k-ohm resistor. (2 marks)
A cell of EMF $1.5$ V and internal resistance $0.30$ ohm drives $0.40$ A. Find the terminal pd. (2 marks)

Solutions

Six short questions covering the Electric circuits module.

Step 1: Q1 - Definition of electric current

Current is defined in terms of the rate at which charge flows past a point in a circuit. This definition underpins the equation $I = Q/t$ and the drift-velocity model $I = nAvq$ .

The rate of flow of electric charge.

Final answer: Electric current is the rate of flow of electric charge.

Step 2: Q2 - Charge from current and time

Rearranging $I = Q/t$ gives $Q = It$ . Both the current and the time are given directly, so one substitution gives the total charge that passes.

Q = It = 4.0 \times 30 = 120\,\text{C}

Final answer: $120\,\text{C}$ .

Step 3: Q3 - Resistance from resistivity

The resistivity equation relates the resistance of a conductor to its material constant, length and cross-sectional area. Substituting the given values and simplifying the powers of ten gives the resistance.

R = \dfrac{\rho L}{A} = \dfrac{(1.6 \times 10^{-8})(1.0)}{4.0 \times 10^{-7}} = 0.040\,\text{ohm}

Final answer: $0.040\,\Omega$ .

Step 4: Q4 - Combined resistance of two parallel resistors

For resistors in parallel, the reciprocals of the individual resistances add to give the reciprocal of the combined resistance. With two equal $4.0\,\Omega$ resistors, the combined resistance is simply half of one.

\frac{1}{R} = \frac{1}{4.0} + \frac{1}{4.0} = \frac{2}{4.0} \implies R = 2.0\,\text{ohm}

Final answer: $2.0\,\Omega$ .

Step 5: Q5 - Output voltage of a potential divider

The potential divider equation gives the voltage across the lower resistor as a fraction of the supply. The fraction is the ratio of the lower resistance to the total resistance.

V_{out} = V_{in} \times \dfrac{R_2}{R_1 + R_2} = 10 \times \dfrac{4.0}{1.0 + 4.0} = 10 \times \dfrac{4.0}{5.0} = 8.0\,\text{V}

Final answer: $8.0\,\text{V}$ .

Step 6: Q6 - Terminal potential difference with internal resistance

The lost volts equal $Ir$ , where $I$ is the current and $r$ is the internal resistance. The terminal pd is therefore less than the EMF by this amount, and the drop grows as the current increases.

V = \varepsilon - Ir = 1.5 - 0.40 \times 0.30 = 1.5 - 0.12 = 1.38\,\text{V}

Final answer: $1.38\,\text{V}$ .

Sources & how we know this

Pearson Edexcel A-Level Physics (9PH0) specification — Pearson Edexcel (2015)