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

Series and parallel circuits

The idea

In a series circuit the current is the same through each component, the total potential difference is shared between components, and the total resistance is the sum of the resistances: R = R₁ + R₂. In a parallel circuit the potential difference across each branch is the same, the total current is the sum of the branch currents, and the total resistance is less than the smallest individual resistance.

Decide whether components are in series or parallel.
Apply the rule for current and potential difference.
Add resistances in series.

Watch out Adding a resistor in parallel decreases the total resistance.

See it worked

Worked example

A 4 Ω and a 6 Ω resistor are in series with a 5 V battery. Find the current.

Total R = 4 + 6 = 10 Ω.
I = V ÷ R = 5 ÷ 10 = 0.5 A.

Answer 0.5 A

Your turn

Question 1Calculator allowed2 marks

Resistors of 3 Ω, 5 Ω and 12 Ω are in series. What is the total resistance in ohms?

Question 2Calculator allowed2 marks

Two branches in parallel carry 0.4 A and 0.6 A. What is the total current from the battery, in amps?

Question 3Calculator allowed1 mark

In a parallel circuit, the potential difference across each branch is:

In past papers

34 official questions in 28 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.