KS3 · Physics
Current in parallel circuits
The wire splits in two. Does one branch grab all the current, does it share out fairly — or does some get lost on the way?
Current in parallel circuits
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change branch 2 — watch all three ammeters
Same lamp in each branch, so the current splits evenly between them. Add the two branch readings and you get exactly what A1 reads next to the cell. Nothing has gone missing.
One cell, two branches, three ammeters. The readings are example values. Switch what's in branch 2, and tap any part of the circuit to find out what it does.
Predict, then check
Picture the circuit before you choose.
Three lamps, X, Y and Z, are each on their own branch of a parallel circuit. On the diagram, X is drawn right beside the cell, Y in the middle, and Z at the far end, so the wires to Z run past Y's branch. Lamp Y breaks. What happens?
Measuring current
What would this ammeter measure?
Think back to the circuit at the top: the cell, junction P where the branches split, junction Q where they rejoin, lamp 1 in branch 1 and a second component in branch 2. Pick an ammeter position, then decide what it measures.
Still to sort
The total current (0)
All of the current through the cell passes through it.
Where the line is: It must be next to the cell, before the current has split at a junction (or after it has rejoined).
The current in one branch (0)
It sits inside a branch, between the junctions at that branch's ends.
Where the line is: Once the current has split at P, a meter only sees the part of the current in its own branch.
Wrongly connected (0)
The ammeter isn't in series, so the current it should measure doesn't all pass through it.
Where the line is: An ammeter is always connected in series — break the circuit, then bridge the gap with the meter.
WHAT YOU'VE LEARNED
A quick recap of today's lesson.
Why the current splits at a junction — and why the pieces always add back up.
What you need to know
- Current is the amount of electric charge that moves through a wire each second. It is measured in amperes (A), often called amps.
- A parallel circuit has more than one complete loop (branch) from one end of the cell to the other. The branches split off and rejoin at junctions.
- At a junction the current splits, and the branch currents add up to the total current through the cell.
- An ammeter is always connected in series: next to the cell to measure the total current, or inside a branch to measure that branch's current.
The big picture
A parallel circuit has more than one complete loop from one end of the cell to the other. At a junction the current splits into the branches, and the branch currents add up to the total current through the cell. Each branch has the same voltage pushing current through it, so its resistance decides its current. An ammeter goes in series: next to the cell for the total, inside a branch for that branch's current.
Key points
Worked example
Problem
(Example values.) A parallel circuit has three branches. The ammeter next to the cell reads 0.70 A. Branch 1 carries 0.20 A. Branches 2 and 3 each contain an identical lamp. What is the current through each of those lamps?
⚠ Watch out
Connecting an ammeter across a lamp, with one lead on each side of it, to measure the lamp's current. That puts the ammeter in parallel. An ammeter always goes in series: break the circuit where you want to measure, and bridge the gap with the ammeter.
Memory hook
Split, then add back. Whatever flows into a junction flows out of it, so the branches always add up to the total.
Check yourself
Can you explain why the ammeter next to the cell reads more than any single branch ammeter — and why that reading drops if one branch's lamp breaks?
Flashcards
(14)What is electric current?
What unit is current measured in?
What makes a circuit a parallel circuit?
What is a junction?
The junction rule
Is an ammeter connected in series or in parallel?
Where does an ammeter go to read the whole current from the cell?
Where do you put an ammeter to measure the current in one branch?
How do you connect an ammeter into a circuit?
What do all the branches of a parallel circuit have in common?
Branch A has a higher resistance than branch B. Which carries the smaller current?
Does a component's distance from the cell change its current?
One lamp in a parallel circuit breaks. What happens to the lamps in the other branches?
How do you read a parallel circuit drawn in an odd layout?
Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.
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How this lesson was checked. This KS3 Physicslesson was published through Lightbulb Learning's human-designed editorial process — the educational standards, accuracy rules and publication checks it must pass were authored and approved by Philip Halpin. It passed subject-specific assessment, automated educational checks and technical publication verification before going live (publication checks completed 1 October 2026). Published pages are monitored, human spot-checking is ongoing across the lesson library, and anything found wrong is corrected or withdrawn. How our lessons are made and checked. Spotted a mistake? Email hello@lightbulblearning.co and we'll review it.