Circuit Symbols
Every common circuit symbol on one chart, with what each component does, so you can read and draw any circuit diagram.
| Component | What it does |
|---|---|
| Cell / battery | Pushes current round the circuit. The long line is the positive (+) terminal. |
| Lamp | Glows when current flows through it. |
| Switch | Breaks (open) or completes (closed) the circuit. |
| Resistor / variable resistor | Limits the current; a variable resistor lets you change how much. |
| Fuse | Melts and breaks the circuit if the current gets too big. |
| Ammeter | Measures current in amps. Connected in series. |
| Voltmeter | Measures potential difference in volts. Connected in parallel across a component. |
| Diode / LED | Lets current flow one way only (in the direction of the triangle); an LED also gives out light. |
| LDR | Light-dependent resistor: resistance falls as light gets brighter. |
| Thermistor | Resistance falls as temperature rises (NTC thermistor). |
| Motor | Turns electrical energy into movement. |
| Capacitor | Stores charge for a short time, e.g. in a camera flash. |
How to draw a circuit diagram
- Draw the wires as straight lines with square corners, using a ruler.
- Put the cell or battery in first, then add each component with its symbol, leaving no gaps in the loop.
- Components in one loop are in series; components on separate branches are in parallel.
- Add meters last: ammeters in series with what they measure, voltmeters in parallel across it.
Worked example
A torch has 2 cells, a switch and a lamp in one loop. Draw a battery symbol (two cells), a switch and a lamp joined in a rectangle. To measure the current through the lamp, add an ammeter anywhere in the same loop. To measure the potential difference across the lamp, connect a voltmeter on its own branch from one side of the lamp to the other. With a 3 V battery and a 6 Ω lamp, the ammeter reads I = V ÷ R = 3 ÷ 6 = 0.5 A.
Build these circuits and watch the current flow in the Circuit Builder, or work out V = IR and power with the Physics Formulas calculator and the AP Physics 1 equation sheet.
Frequently asked questions
What is the symbol for a resistor?
A small rectangle in the wire in the UK and Europe (IEC symbol). In the US the same resistor is drawn as a zigzag line.
Which side of a cell symbol is positive?
The longer, thinner line is the positive terminal and the shorter, thicker line is the negative terminal. Conventional current flows out of the positive side.
What is the difference between a cell and a battery symbol?
A cell is one long line and one short line. A battery is two or more cells joined together, drawn as repeated pairs (often with a dashed line between them).
How do you connect an ammeter and a voltmeter?
An ammeter goes in series, in line with the component, so the same current flows through it. A voltmeter goes in parallel, across the component, to compare the energy either side of it.
