Circuit symbols and building circuits

Circuit diagrams use symbols so anyone, anywhere, can build the same circuit.

Practise this lesson free (7 questions)

Circuit symbols

Scientists draw circuits with standard symbols and straight lines for wires.
ComponentHow the symbol is drawnWhat it does
CellA long thin line and a short thick lineProvides the push (p.d.)
BatteryTwo or more cells joinedA bigger push
Lamp (bulb)A circle with a cross insideLights up
SwitchA gap in the wire with a hinged lineOpens or closes the circuit
ResistorA small rectangleReduces the current
AmmeterA circle with A insideMeasures current
VoltmeterA circle with V insideMeasures potential difference

Series circuits

In series everything is in one loop. One switch turns everything on or off.
If one lamp breaks, the circuit is broken and all go out.
Adding more lamps makes each one dimmer, because the p.d. is shared and the current is smaller.
Cells in series add up: three 1.5 V cells give 4.5 V.
3 × 1.5 V = 4.5 V switch(closed) 2.25 V 2.25 V One loop: one switch controls both lamps
Series circuit: three 1.5 V cells give 4.5 V, shared by two identical lamps (2.25 V each).

Parallel circuits

In parallel there are separate branches. Each branch gets the full p.d. of the battery.
A switch in one branch controls only that branch. If one lamp breaks, the others stay on.
The currents in the branches add up to the current from the battery.
The lights and sockets in a house are wired in parallel, so each works on its own.
switch for this branch only Each branch gets the full p.d.
Parallel circuit: each lamp is on its own branch, with the full p.d.
Worked example

Three 1.5 V cells are joined in series to light two identical lamps in series. What is the p.d. across each lamp?

  1. Total p.d. = 3 × 1.5 = 4.5 V
  2. Two identical lamps share it equally.
  3. 4.5 ÷ 2

Answer: 2.25 V

Key idea

Series: one loop, current the same everywhere, p.d. shared, one break stops everything. Parallel: branches, each gets the full p.d., branch currents add up, branches work independently.

Common mistakes
Quick check

Try two quick questions

See if it has sunk in. Answers are marked straight away.

Extra practice

2 more questions

Try each one, then tap to check.

  1. Three 1.5 V cells are joined in series. What is the total p.d.?

    Show the answer

    Answer: 4.5 V

    In series, add them: 3 × 1.5 = 4.5 V

  2. A parallel circuit has two branches carrying 0.25 A and 0.5 A. What current flows from the battery?

    Show the answer

    Answer: 0.75 A

    The branch currents add up: 0.25 + 0.5 = 0.75 A

Check you have got it

Answer 7 quick questions with instant marking. If you get one wrong, GCSE-ready shows you why and gives you another go. It is free, and you do not need an account.

Practise this lesson free (7 questions)All KS3 Science lessons

Video for this lesson coming soon. Subscribe on YouTube

Sources and references

Checked by the GCSE-ready editorial team, 17 October 2026. Last updated 2 October 2026. Spotted a mistake? Tell us and we will fix it.

Related lessons