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LearnCambridge97022025–2027Paper 2 · AS Level Structured QuestionsElectricity

Paper 2 · Module

Electricity

3 subtopics≈ 95 min in total

Start the module: Electric current Open graphing calculator

Electric current
Current is the rate of flow of charge, $I=\dfrac{\Delta Q}{\Delta t}$ . Charge comes in whole multiples of the elementary charge $e=1.60\times10^{-19}$ C. In a conductor, current depends on the number density of charge carriers, their charge and their drift velocity: $I=Anvq$ . Electrons drift slowly, but the signal travels almost instantly.
≈ 30 min
Potential difference and power
The potential difference across a component is the energy transferred from electrical to other forms per unit charge: $V=\dfrac WQ$ , so $1$ V $=1$ J C⁻¹. Electrical power is $P=VI$ ; combining with $V=IR$ gives $P=I^2R=\dfrac{V^2}R$ . Choose whichever form uses the quantities you know.
≈ 30 min
Resistance and resistivity
Resistance is $R=\dfrac VI$ . A metal at constant temperature obeys Ohm's law: current is proportional to p.d. A wire's resistance depends on its material, length and area: $R=\dfrac{\rho L}A$ , where the resistivity $\rho$ is a material property. Filament lamps, diodes, thermistors and LDRs have non-ohmic, changing resistances.
≈ 35 min