KS3 · Physics

Electric current

Flick a switch and a lamp lights instantly — yet each electron in the wire creeps along only a few millimetres a second. How can that be?

Electric current · A series loop

Three ammeters, one loop. Do they agree?
+−AAAA1A2A3electron flow0.30 A0.30 A0.30 A

View: 1 lamp. Showing 2 layers: Series loop, One lamp

View

Explore

switch 1 → 2 → 3 lamps and read all three ammeters

One lamp. A1 is before the lamp on the electrons’ way round; A2 and A3 are after it. All three read 0.30 A — the lamp hasn’t used any current up.

Current is measured in amperes — amps for short, symbol A. The readings are example values for one cell and identical lamps.

What the cell is doing

?

Reason it through

How does a cell get charge flowing all the way round a circuit?

Link 1 of 4

First link · your turn

Something has to happen inside the cell first. What?

2
Locked — reveal the link above first
3
Locked — reveal the link above first
4
Locked — reveal the link above first

The instant-lamp puzzle

How does the lamp know to light straight away?

A lamp is joined to a cell by several metres of wire. You close the switch and the lamp lights immediately — yet each electron in the wire creeps along only a few millimetres every second.

How can the lamp light instantly? Pick the idea closest to what you think right now.
How sure are you?

Relationship matrix

Tap any cell to reveal it. Tap a column header to read one property down every item.

Rope modelRiver model
The cellkeeps the charge moving
The moving chargethe current
A componente.g. a lamp

Each cell hides a short answer and the reason behind it. Predict before you tap.

Your turn

Correct, or needs fixing?

Is each set-up or label correct, or does it need fixing?

Still to sort

Correct (0)

It would work, or it is labelled the right way round.

Where the line is: An ammeter anywhere IN the loop is fine. A battery needs cells of the same type AND lined up the same way — one without the other isn’t enough.

Needs fixing (0)

Something is in the wrong place or the wrong way round.

8 of 8 still to sort.

Pick each card, then choose where it goes. Read the reason when it’s checked.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

A flow of charge round a loop — and why a lamp never uses it up.

What you need to know

  • Electric current is the flow of electric charge round a circuit, measured in amperes (amps, A).
  • In metal wires the moving charges are electrons: tiny, negatively charged and free to move.
  • A cell uses a chemical reaction to push electrons out of its negative terminal and pull them in at its positive terminal.
  • An ammeter measures current. It is connected in series, and in a series circuit the current is the same everywhere.

The big picture

Electric current is a flow of charge round a complete circuit. In metal wires the moving charges are electrons. A cell pushes electrons out of its negative terminal and pulls them in at its positive terminal, so charge flows one way round the loop. Current is measured in amperes (amps, A) with an ammeter connected in series. In a series circuit the current is the same everywhere — components don’t use it up — and adding a lamp lowers it everywhere at once.

Key points

1Current is a flow of charge. Its unit is the ampere (amp), symbol A.
2Every cell has a positive and a negative terminal. In the symbol, the longer, thinner line is positive and the shorter, wider line is negative.
3Two or more cells make a battery: same type, lined up positive terminal to negative terminal.
4Electrons are in every part of a circuit even when it is off. Switch on and they all start moving at once, so a lamp lights straight away — even though each electron moves only a few millimetres per second.
5If there is a gap in the circuit, electrons can’t flow across it, so there is no current.
6A series circuit is one complete loop. The current is the same everywhere in it — components don’t use current up.
7Adding a lamp or resistor anywhere in a series loop lowers the current everywhere. Changing the order of the components doesn’t change the current.
8An ammeter (a circle with A inside) goes in series, can go anywhere in the loop, and doesn’t change the current it measures.

Worked example

Problem

A series circuit has a cell, a lamp and a resistor in one loop, with three ammeters: P between the cell and the lamp, Q between the lamp and the resistor, and R between the resistor and the cell. P reads 0.24 A. (a) What do Q and R read? (b) The lamp and the resistor swap places. What do the ammeters read now?

⚠ Watch out

Thinking a lamp uses up current, so an ammeter after the lamp should read less than one before it. In a series circuit every ammeter shows the same reading: the same number of electrons comes out of the lamp as goes in.

🧠

Memory hook

Think of a bike chain. Push the pedal and every link moves at the same moment — and the chain isn’t any shorter after the back wheel than before it. Current is like that: all moving together, same all the way round, never used up.

✓

Check yourself

Cover the page. In a series circuit, an ammeter just before a lamp reads 0.4 A. What does an ammeter just after the lamp read — and can you explain why in one sentence?

Flashcards

(14)
What is electric current?
The flow of electric charge round a circuit.
What is the unit of current, and its symbol?
The ampere (amp), symbol A.
What are the charges that flow in a metal wire?
Electrons — tiny, negatively charged particles.
Why are metals good electrical conductors?
Their electrons are free to move.
What does a cell do to make charge flow?
Its chemical reaction makes one terminal positive and one negative. It pushes electrons out of the negative terminal and pulls them in at the positive terminal.
Cell symbol: which line is the positive terminal?
The longer, thinner line. The shorter, wider line is negative.
What makes a battery, and how must its cells be joined?
Two or more cells of the same type, lined up so each positive terminal joins the next cell’s negative terminal.
Are there electrons in a circuit that is switched off?
Yes — in the wires, the cell and the components. They just aren’t flowing.
Why does a lamp light the instant you switch on?
Electrons everywhere in the circuit start moving at the same time.
Roughly how fast does each electron move along a wire?
Slowly — a few millimetres each second.
What happens to the current if there is a gap in a circuit?
Electrons can’t flow across the gap, so there is no current.
How does the current compare at different points in a series circuit?
It is the same everywhere in the loop.
How is an ammeter connected, and what is its symbol?
In series, anywhere in the loop, so all the current passes through it. Symbol: a circle with A inside.
What happens to the current when you add a lamp to a series circuit?
It decreases everywhere in the loop — on both sides of the new lamp.

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 30 September 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.