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Electric current and voltage


Circuit symbols

We use circuit symbols to draw diagrams of electrical circuits, with straight lines to show the wires. The diagram shows some common circuit symbols.

Switch - two circles connected by a line. If the line connects the circles, the switch is closed. If it is only connected to one circle the switch is open. A cell - two vertical lines, one thin and one shorter and thicker. A battery - two cells connected by a dotted line. A lamp - a circle with a cross in it. A voltmeter - a letter V inside a circle. An ammeter - a letter A inside a circle. A resistor - a rectangle. A variable resistor - a rectangle with an arrow through it at 45 degrees. A motor - a letter M inside a circle.

Cells and batteries

Notice the difference between the symbol for a cell and the symbol for a battery? The battery is made from joining cell symbols together.

Think of what we usually call a single battery, like the type you put in a torch. In physics, each of these is actually called a cell - it is only when you have two or more of these cells connected together that you call it a battery.

Circuit diagrams

The idea of a circuit diagram is to use circuit symbols instead of drawing each component in the circuit. Always try to make the wires straight lines, and don't be tempted to make them wiggly.

The whole point is to make it easier to see what is connected to what. Here you can see how the symbols for a cell (not a battery!) and a lamp look in a circuit diagram.

Shows a circuit with a cell and a lamp, and then the same circuit drawn as a circuit diagram

If you have to draw a circuit diagram from scratch, it is usually easier to draw the circuit symbols first, and then add all the wires. If you have to draw wires to join circuit symbols that are already shown, use a ruler and don't let the wires cross each other.


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