Page 149 - Science Coursebook

10.4 Conductors and insulators

Electric current
Electricity makes a lamp light up. ‘Electricity’ is a vague
word. It is better to talk about electric current. We say:
The lamp lights up because there is an electric current in
the circuit.
Two things are needed for there to be an electric current:

• a complete circuit of metal around which the current
can flow

• a cell (a battery) to make the current flow.

A switch breaks a circuit to stop the current flowing.
The picture shows three components connected up to
make a circuit.

Question
1 Study the picture of the circuit. The electric current

flows from the positive (+) end of the cell. Which
component does it reach first, the switch or the lamp?

Circuit symbols cell

Scientists and engineers draw circuit diagrams to show how switch
different components are connected together in an electric circuit.

They use a circuit symbol for each type of component. Because
everyone uses the same symbols, they can understand each other’s
diagrams. Computers can understand the diagrams, too.
The diagram shows the same circuit as in the picture above.
• Each symbol is labelled with the name of the component lamp
it represents.
• The wires joining the components are shown as lines.

Question

2 Study the circuit diagram. Draw the circuit symbols
for a cell, a switch and a lamp.
3 Which part of the symbol for a cell represents the
positive end, the long line or the short line?

Summary
• Metals are good conductors of electricity. Non-metals are usually
insulators.
• A complete circuit is needed for a current to flow.

10 Electricity 147