GCSE Combined Science revision · Physics: energy, electricity, particles and atoms

Current, voltage and resistance

The idea

Electric current is the rate of flow of charge: Q = It. The current through a component depends on the potential difference across it and its resistance: V = IR. An ohmic conductor at constant temperature has a straight-line I–V graph. A filament lamp's resistance rises as it heats up. A diode lets current flow in one direction only. A thermistor's resistance falls as temperature rises; an LDR's resistance falls as light intensity rises.

Pick the equation: Q = It or V = IR.
Use amps, volts, ohms and seconds.
Read the I–V graph shape for the component.

Watch out An ammeter goes in series; a voltmeter goes in parallel.

See it worked

Worked example

A current of 0.5 A flows through a 12 Ω resistor. Calculate the potential difference across it.

V = IR = 0.5 × 12.
= 6 V.

Answer 6 V

Your turn

Question 1Calculator allowed2 marks

A current of 2 A flows for 30 s. How much charge flows, in coulombs?

Question 2Calculator allowed2 marks

A 6 V battery drives a current of 0.3 A through a lamp. What is the lamp's resistance in ohms?

Question 3Calculator allowed1 mark

How does a thermistor's resistance change as temperature increases?

In past papers

89 official questions in 48 papers since 2018. The latest:

All GCSE Combined Science past papers

GCSE Science Pro

£119 once

At least 12 months of access

By paying you agree to our Terms and get access straight away, which ends your 14-day cancellation right.

Start free

No VAT is charged.