KS3 · Physics

Building a series circuit

Open a switch on one side of a circuit. Does the motor on the far side keep running? Hold on to your answer — this lesson settles it.

Read the circuit

One loop, six components

Showing 2 layers: Circuit, Trace the loop

Layers

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tap a symbol, then trace the loop

Start at one end of the battery and follow the wire: ammeter, resistor, motor, lamp, switch — and you arrive back at the other end of the battery. Your finger never had to choose a way to go. One loop, no junctions: that's a series circuit.

A series circuit diagram: a battery of two cells, a closed switch, a lamp, a motor, a resistor and an ammeter, all joined in one loop.

What does an open switch do?

One switch, the far side of the loop

A series circuit goes battery → switch → lamp → motor → back to the battery. The switch sits right beside the battery, and the motor is on the far side of the loop, closest to the battery's other end. Someone opens the switch.

What happens to the lamp and the motor? Pick the idea closest to what you think right now.

Only the lamp goes off, because it's the component right next to the switch. The motor is further round, so it keeps running.The lamp goes off, but the motor keeps running. It's joined to the other end of the battery, so it still gets electricity from there.The lamp and the motor both go off. The open switch makes a gap, and a gap anywhere in the loop stops the electricity everywhere.

How sure are you?

I'm sureI think soI'm guessing

Only the lamp goes off, because it's the component right next to the switch. The motor is further round, so it keeps running.

This is a common misconception

Lots of people picture a switch as a tap for whatever is beside it. But a series circuit is one loop, and electricity passes through every component one after the other — the switch included. Open the switch and you put a gap in the only path there is. With a gap, the circuit isn't complete, so electricity can't flow anywhere in the loop: the lamp AND the motor both stop.

The lamp goes off, but the motor keeps running. It's joined to the other end of the battery, so it still gets electricity from there.

This is a common misconception

A battery has two ends, so this one feels reasonable. But electricity doesn't come out of each end separately to feed the nearest component. It flows round one complete loop, from one end of the battery to the other. The open switch breaks that loop, so there's no complete circuit for the motor either — it stops too.

The lamp and the motor both go off. The open switch makes a gap, and a gap anywhere in the loop stops the electricity everywhere.

This matches the evidence

Exactly right. A series circuit has one loop and no junctions, so every component depends on the whole loop being complete. One gap — wherever it is — stops electricity flowing through all of them.

Series circuit, one loop: a gap anywhere stops electricity flowing through every component. Closing the switch presses its metal pieces together, which completes the circuit again.

Predict, then check

Picture each diagram as a rectangle with one component on each side.

Ana and Ben each draw a diagram using the same battery, switch, lamp and motor. Ana puts the battery on the top side, the switch on the right, the lamp on the bottom and the motor on the left. Ben puts the motor on the top, the battery on the right, the switch on the bottom and the lamp on the left. Have they drawn the same circuit?

Building a series circuit from its diagram

Diagram on one side, components on the other. Work round the loop one wire at a time.

Count what you needCount the components on the diagram, and the wires. Collect exactly those before you start, so nothing is missing halfway round.
Lay them out in orderPut the components on the bench in the same order as the diagram. The order is what the diagram is telling you — get it right here and the rest is easy.
Start at one componentStart at any component. The battery is often the easiest place. Connect it to the next component in the diagram with one wire.
Repeat round the loopNow connect that component to the next one, then the next, one wire at a time, until the last component is wired back to where you started.

Drawing it neatly

Right or wrong in a circuit diagram?

Pick a feature, then decide: right or wrong for a series circuit diagram?

Still to sort

Right (0)

Belongs in a correct series circuit diagram.

Wrong (0)

Needs fixing before the diagram is correct.

Where the line is: Gaps are the trap. A gap is right in only two places: between the terminals of each cell, and in an open switch. Anywhere else, a gap is wrong.

8 of 8 still to sort.

Circuit diagrams are drawn with a sharp pencil, a rubber and a ruler. Decide whether each feature belongs in a correct series circuit diagram.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

One loop, no junctions — and a diagram that cares about order, not position.

What you need to know

What makes a circuit a series circuit: one complete loop, no junctions, with electricity passing through each component in turn.
How to read the symbols in a circuit diagram — and which components have to be connected the correct way round.
How to build a series circuit from a diagram, and how to draw a neat diagram of a circuit you've built.

The big picture

A series circuit is one complete loop from one end of a battery to the other, with no junctions. Electricity passes through every component one after the other, so a gap anywhere — such as an open switch — stops it flowing through all of them. Circuit diagrams use simple symbols and show the order of the components, not their positions. You build a circuit from a diagram by working round the loop one connection at a time, and you draw one by following the circuit in one direction with a ruler.

Key points

1Series circuit = one complete loop from one end of the battery to the other, with no junctions. Electricity passes through every component, one after the other.

2A complete circuit has no gaps. Open a switch anywhere in the loop and electricity stops flowing through every component; closing it presses the metal pieces together and completes the circuit.

3Symbols: lamp = circle with a cross; motor = circle with M; ammeter = circle with A; voltmeter = circle with V; resistor = rectangle; switch = two small circles, with a line touching both when closed and a gap when open.

4A cell is two parallel lines: long thin line positive, short wide line negative. Cells joined together make a battery, with each positive terminal connected to the negative terminal of the next cell.

5Cells, ammeters and voltmeters have positive and negative terminals, so they must be connected the correct way round.

6A circuit diagram shows the order of the components, not their positions. Change where things sit but keep the order, and it's the same circuit.

7Drawing rules: ruler and sharp pencil; straight horizontal or vertical wires; no gaps except between a cell's terminals and in an open switch; wires never through a symbol; battery usually at the top or left.

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Worked example

Problem

On the bench is a finished circuit. Starting from the battery (two cells) and following the wires round, you meet a lamp, then a resistor, then an open switch, and then you're back at the battery. Draw its circuit diagram.

⚠ Watch out

Thinking an open switch only turns off the component next to it. A series circuit has only one loop, so a gap anywhere — at the switch or anywhere else — stops electricity flowing through every component in it.

🧠

Memory hook

Finger on the battery, trace the loop. If your finger never has to choose which way to go, it's a series circuit. Order matters — position doesn't.

✓

Check yourself

Cover the page and draw, from memory, the symbols for a cell, an open switch, a lamp, a motor, a resistor and a voltmeter. Which line of your cell is positive?

Flashcards

(14)

What makes a circuit a series circuit?

It is one complete loop from one end of the battery to the other, with no junctions. Electricity passes through every component, one after the other.

What is a complete circuit?

A circuit with no gaps, so electricity is able to flow round it.

What does closing a switch actually do?

It presses the metal pieces together, which completes the circuit.

In a cell symbol, which line is the positive terminal?

The longer, thinner line. The shorter, wider line is the negative terminal.

What is a battery, and how are its cells joined?

Two or more cells joined together, with each positive terminal connected to the negative terminal of the next cell.

Ammeter or voltmeter? How do you tell the symbols apart?

Both are circles. An ammeter has an A inside; a voltmeter has a V inside. A voltmeter measures voltage.

Lamp or motor? How do you tell the symbols apart?

Both are circles. A lamp has a cross inside; a motor has a capital M inside.

How are an open switch and a closed switch drawn?

Both are two small circles. Closed: a line touches both circles. Open: there's a gap — the line doesn't touch the second circle.

Name the component drawn as a plain rectangle.

A resistor.

Which components must be connected the correct way round?

Cells, ammeters and voltmeters — they each have a positive and a negative terminal.

Does a circuit diagram show where components sit, or the order they come in?

The order. Move a component to a different place without changing the order and it's still the same circuit.

Building from a diagram: how do you connect the components?

Start at any component (often the battery), wire it to the next one, then repeat for each component in turn round the loop.

What do you check once you've built a series circuit?

That it matches the diagram, with no gaps and one single loop.

Where is the battery usually drawn in a circuit diagram?

At the top or on the left.

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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One switch, the far side of the loop

Right or wrong in a circuit diagram?

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