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Current Electricity

Still about one question a paper, though smaller than in the early papers. Kirchhoff's laws, bridges, meters and cells; many answers are numbers, so no option will catch a slip.

Questions in the bank
230
q/paper in 2025–26
1.28
Numeric answer
43%
Notes pages
8

Tier: Core

When you’ll see it

A circuit of resistors and cells, a wire stretched or heated, a meter bridge or potentiometer at balance, or a capacitor or inductor in a DC circuit.

How this chapter is tested

Current Electricity is a core chapter, set about once a paper; it once carried cornerstone weight and has shrunk since. Many of its questions ask for a number and come with a circuit, so the first skill is redrawing: name the junctions, merge points joined by plain wire, and look for symmetry or a balanced bridge before writing any equation.

After that, most questions need one of three tools: Ohm's law with the series and parallel rules, Kirchhoff's two laws, or a ratio at balance in a meter bridge or potentiometer. Power questions pick the form of I²R or V²/R that holds fixed what the circuit holds fixed.

Marks are lost on small things: a cell's internal resistance left out, a stretched wire's resistance scaled by n instead of n², a real voltmeter read as if it were ideal, or current sent through a capacitor branch in steady state. The steady-state pages lean on Electrostatics, and the LR circuits meet Electromagnetic Induction.

The sub-skills

The distinct skills inside the chapter, in the order to learn them.

  • Current and drift velocity

    I = dq/dt, with charge as the area under an I–t graph; I = neAv, the electrons drifting slowly against the field.

  • Resistance and temperature

    R = ρl/A with ρ set by the material and its temperature; a wire stretched to n times its length has n² times the resistance.

  • Equivalent resistance

    Series resistances add, parallel ones add as reciprocals; redraw a network by merging shorted points and using symmetry about where the current enters and leaves.

  • Kirchhoff's laws and the bridge

    Junction and loop laws, current and voltage dividers, and the balanced Wheatstone bridge with P/Q = R/S.

  • Cells

    I = ε/(R + r) and terminal voltage ε − Ir, or ε + Ir for a cell being charged; cells in parallel weight their emfs by 1/r.

  • Meters, meter bridge and potentiometer

    A real voltmeter reads low; the meter bridge and the potentiometer measure at balance, when the galvanometer carries no current.

  • Power and heating

    P = VI = I²R = V²/R; off its rated supply a device keeps its resistance, not its wattage; in series the lower rating glows more.

  • Capacitors and inductors in DC circuits

    Just after switching a capacitor acts as a wire and an inductor as a gap, long after the reverse; in between both change with time constant RC or L/R.

Traps to expect

Distractor shapes this chapter reuses. The Traps page covers the ones that cut across chapters.

  • Internal resistance left out

    The current is ε/(R + r). Dividing ε by R alone forgets the cell's own resistance.

  • A stretched wire scaled by n

    Stretching to n times the length also thins the wire n times in area, so R grows as n². Scaling by n alone is the commonest wrong option.

  • A real voltmeter read as ideal

    A real voltmeter lowers the resistance it sits across, so it reads below the ideal divider value.

  • Current in a capacitor branch

    In steady state a capacitor branch carries no current, and a resistor in that branch drops no voltage. Remove the branch before finding the currents.

Learn it before you drill it

This chapter has full teaching notes — foundations, worked examples, self-checks and a mastery check for each page. Read the notes once, then drill page by page below.

Current Electricity notes

Drill every Current Electricity question

230 questions from the bank, across 8 subtopics.

Drill the 230 questions

Drill one subtopic at a time

The 8 subtopics, in teaching order.

Related playbooks

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