IGCSE Physics · 0625

IGCSE Physics: Electric Circuits Practice Questions

Circuit questions combine a formula and a rule you must recall. These worked examples cover Ohm's law calculations, how current behaves in series and parallel, and total resistance in series.

What you need to know

Ohm's law: voltage equals current times resistance, V equals I times R.
In a series circuit the current is the same everywhere; the voltages add up.
In a parallel circuit the current splits between branches; each branch has the full voltage.
Total resistance in series is found by adding the resistances.

A series circuit: the ammeter reads the same current at any point.

Practice questions with answers

Question 12 marks

A component has a voltage of 12 V across it and a current of 3 A through it. Calculate its resistance.

Rearrange V = I times R to R = V divided by I. R = 12 divided by 3 = 4 ohms.

Mark schemeCorrect rearrangement R = V over I (1). Answer 4 ohms with unit (1).

Common mistakeMultiplying instead of dividing, or leaving off the unit ohms.

Exam tipRearrange the formula before substituting numbers, and always give the unit.

Question 23 marks

Describe how the current behaves in a series circuit compared with a parallel circuit.

In a series circuit the current is the same at every point in the circuit. In a parallel circuit the current from the source splits between the branches, so the current in each branch may be smaller and the branch currents add up to the total.

Mark schemeSeries: current the same everywhere (1). Parallel: current splits between branches (1). Branch currents add to the total (1).

Common mistakeSaying current is used up as it goes round. Current is not used up.

Exam tipAddress both series and parallel. A comparison needs both cases.

Question 32 marks

Two resistors of 5 ohms and 7 ohms are connected in series. Calculate the total resistance.

In series, resistances add. Total resistance = 5 plus 7 = 12 ohms.

Mark schemeMethod, add the resistances (1). Answer 12 ohms (1).

Common mistakeUsing the parallel formula when the resistors are in series.

Exam tipSeries resistors simply add. Only use the reciprocal formula for parallel resistors.

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Frequently asked questions

What is Ohm's law?

Ohm's law states that voltage equals current times resistance, V equals I times R, for a component at constant temperature.

How does current behave in a series circuit?

The current is the same at every point in a series circuit. It is not used up as it flows around.

Where do you connect an ammeter and a voltmeter?

An ammeter is connected in series to measure current. A voltmeter is connected in parallel across a component to measure voltage.

How do you find total resistance in series?

Add the individual resistances together. For example, 5 ohms plus 7 ohms gives 12 ohms.

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