What does Eduqas electricity and DC circuits cover?

It covers conduction of electricity with current as the rate of flow of charge and the equation I = nAvq, resistance with Ohm's law, I-V characteristics and resistivity, DC circuits with Kirchhoff's two laws, series and parallel resistors, internal resistance and the potential divider, capacitance with stored charge and energy and exponential charge and discharge, and solids under stress with Hooke's law, stress, strain, the Young modulus and strain energy.

Which equations recur most across this content?

Current $I = \frac{\Delta Q}{\Delta t}$ and $I = nAvq$, resistance $R = \frac{V}{I}$ and resistivity $R = \frac{\rho L}{A}$, power $P = VI = I^2 R = \frac{V^2}{R}$, the electromotive force relation $\varepsilon = I(R + r)$ and terminal voltage $V = \varepsilon - Ir$, the potential divider $V_\text{out} = V_\text{in}\frac{R_2}{R_1 + R_2}$, capacitance $C = \frac{Q}{V}$ with energy $\frac{1}{2}CV^2$ and discharge $Q = Q_0 e^{-t/RC}$, and the materials trio $\sigma = \frac{F}{A}$, $\varepsilon = \frac{\Delta L}{L}$, $E = \frac{\sigma}{\varepsilon}$.

What is the most common mistake in this content?

Swapping the series and parallel rules between resistors and capacitors. Resistors add in series and combine by reciprocals in parallel; capacitors do the opposite. Close behind are using the diameter instead of the radius in a wire's cross-sectional area, forgetting the lost volts $Ir$ inside a real cell, dropping the minus sign in the capacitor discharge exponent, and confusing the force constant with the Young modulus.

How is internal resistance examined in Eduqas Physics?

Typically a cell drives a current through a known external resistor and you find the current and terminal voltage from $\varepsilon = I(R + r)$ and $V = \varepsilon - Ir$. A common variant gives two loads or a graph of terminal voltage against current, from which the electromotive force is the intercept and the internal resistance is the magnitude of the gradient.

How should I revise electricity and DC circuits?

Drill the circuit-analysis routine: label currents with Kirchhoff's first law, write loop equations with the second law, and combine resistors correctly. Master internal resistance and the potential divider, then the exponential capacitor discharge with logarithms. For materials, practise the Young modulus calculation and reading stress-strain graphs. The specified practicals on resistivity, capacitor discharge and the Young modulus recur in the written papers.

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Eduqas A-Level Physics Electricity and DC circuits: conduction, resistance, circuits, capacitance and materials

A deep-dive Eduqas A-Level Physics guide to the electricity and materials content within Component 2. Covers conduction and drift velocity, resistance and resistivity, DC circuits with Kirchhoff's laws and internal resistance, capacitance with exponential discharge, and solids under stress with the Young modulus, with the calculations Eduqas repeats.

Generated by Claude Opus 4.816 min readA720QS Component 2Updated 2026-06-02

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

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What this module actually demands
Conduction, resistance and circuits
Capacitance and materials
How this module is examined
Check your knowledge

What this module actually demands

The electricity and materials content sits within Component 2 (Electricity and the Universe). It starts from what an electric current is at the level of charge carriers, builds through resistance and full circuit analysis, adds the capacitor as an energy store, and covers how solids deform under load. The examiners reward fluent circuit analysis, careful exponential work, and precise definitions, and the specified practicals on resistivity, capacitor discharge and the Young modulus recur across the written papers.

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

Conduction, resistance and circuits

Conduction of electricity defines current as the rate of flow of charge, derives and uses $I = nAvq$ , explains drift velocity, and uses the carrier density to distinguish conductors, semiconductors and insulators. Resistance and resistivity states Ohm's law, sketches the I-V characteristics of an ohmic conductor, a filament lamp and a diode, uses $R = \frac{\rho L}{A}$ , and explains the temperature dependence of metals and thermistors.

DC circuits and Kirchhoff's laws applies Kirchhoff's two laws, combines resistors in series and parallel, handles electromotive force and internal resistance with $\varepsilon = I(R + r)$ , analyses the potential divider, and calculates electrical power and energy.

Capacitance and materials

Capacitance defines $C = \frac{Q}{V}$ , finds the stored energy $\frac{1}{2}CV^2$ , combines capacitors in series and parallel (the reverse of resistors), and analyses exponential charge and discharge with time constant $RC$ . Solids under stress states Hooke's law, defines stress, strain and the Young modulus, finds strain energy as an area, and contrasts ductile, brittle and polymeric behaviour.

How this module is examined

A typical Eduqas profile for this content:

Calculations. Drift velocity from $I = nAvq$ , resistivity from wire data, currents and voltages from Kirchhoff's laws, internal resistance, potential-divider outputs, capacitor charge, energy and exponential discharge, and the Young modulus.
Graph questions. I-V characteristics, terminal-voltage-against-current lines, capacitor discharge curves and logarithmic linearisation, and force-extension and stress-strain graphs.
Explanation and definition. Ohm's law, the filament lamp curve, Kirchhoff's laws as conservation principles, and ductile versus brittle behaviour.
Extended answers. Sensing circuits using thermistors or light-dependent resistors, capacitor timing, and material selection arguments.

Check your knowledge

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

State Ohm's law. (1 mark)
A current of $0.40\ \text{A}$ flows for $90\ \text{s}$ . Find the charge that passes. (2 marks)
Two $4.0\ \Omega$ resistors are connected in parallel. Find their combined resistance. (2 marks)
A $220\ \mu\text{F}$ capacitor is charged to $15\ \text{V}$ . Find the charge stored. (2 marks)
A wire of cross-sectional area $4.0 \times 10^{-7}\ \text{m}^2$ carries a load of $80\ \text{N}$ . Find the stress. (1 mark)
State how capacitors combine in parallel. (1 mark)

Solutions

Six questions covering Ohm's law, charge, parallel resistors, capacitance, stress, and capacitor combinations.

Step 1: Q1 - State Ohm's law

Ohm's law applies to metallic conductors and describes the linear relationship between current and potential difference when temperature is held constant. The relationship breaks down for non-ohmic components such as filament lamps and diodes, whose resistance changes with temperature or voltage.

Final answer: For a metallic conductor at constant temperature, the current is directly proportional to the potential difference.

Step 2: Q2 - Find the charge that passes in 90 s

Electric current is defined as the rate of flow of charge, so $I = \frac{\Delta Q}{\Delta t}$ , which rearranges to $Q = It$ . The charge is simply the current multiplied by the time for which it flows.

Q = It = 0.40 \times 90 = 36\ \text{C}

Final answer: $Q = 36\ \text{C}$ .

Step 3: Q3 - Find the combined resistance of two $4.0\ \Omega$ resistors in parallel

For resistors in parallel, the reciprocals of resistance add. Two equal resistors in parallel always give half the individual resistance, because each carries half the current.

\frac{1}{R} = \frac{1}{4} + \frac{1}{4} = \frac{1}{2}, \quad \text{so}\ R = 2.0\ \Omega

Final answer: $R = 2.0\ \Omega$ .

Step 4: Q4 - Find the charge stored on a $220\ \mu\text{F}$ capacitor charged to $15\ \text{V}$

The definition of capacitance is $C = \frac{Q}{V}$ , which rearranges to $Q = CV$ . Substituting the values, remembering to convert microfarads to farads, gives the stored charge.

Q = CV = 220 \times 10^{-6} \times 15 = 3.3 \times 10^{-3}\ \text{C} = 3.3\ \text{mC}

Final answer: $Q = 3.3\ \text{mC}$ .

Step 5: Q5 - Find the stress in the wire

Stress is defined as force per unit cross-sectional area and is measured in pascals ( $\text{Pa} = \text{N m}^{-2}$ ). Dividing the applied force by the cross-sectional area gives the stress directly.

\sigma = \frac{F}{A} = \frac{80}{4.0 \times 10^{-7}} = 2.0 \times 10^{8}\ \text{Pa}

Final answer: $\sigma = 2.0 \times 10^{8}\ \text{Pa}$ .

Step 6: Q6 - State how capacitors combine in parallel

Capacitors in parallel share the same voltage across their plates, so the total charge stored is the sum of the charges on each capacitor. This means total capacitance equals the sum of the individual capacitances, which is the opposite rule to resistors in parallel.

Final answer: Their capacitances add: $C = C_1 + C_2 + \dots$

Sources & how we know this

Eduqas GCE AS/A Level Physics specification (A720QS) — WJEC Eduqas (2015)