Page 154 - Science Coursebook

10.7 Changing circuits 1

Many electrical appliances use cells (batteries). The X-ray
photograph shows a torch with two batteries inside it. You
can see that the batteries are connected end-to-end – they
are in series.

Question
A torch like this needs two cells to give
A+I 1 What would you observe if the torch had only enough current to light the lamp brightly.
one cell? Explain your answer.

The voltage of a cell
Cells are usually labelled with their voltage. The
label might say ‘1.5 V’. This means that the voltage
of the cell is 1.5 volts. The volt (symbol V) is the unit
of voltage.
A voltmeter is used to measure voltage. To measure
the voltage of a cell, wires are connected from the
ends of the cell to the terminals of the voltmeter.
The positive (red) terminal of the voltmeter should
be connected to the positive terminal of the cell.
1.5v

V
More cells
If two or more cells are connected together in series, their voltages add up. The
diagram shows how to represent two or more cells connected in series, and the value
of their combined voltages. In this diagram, each cell is 1.5 V.
Take care! If you connect two cells back-to-front (positive to positive or negative to
negative), their voltages will cancel out.

1.5 v 3.0 v 4.5 v 0 v
+ − + − + − + − + − + − + − − +

Questions
2 Draw the circuit symbol for a voltmeter.
3 If the torch in the photograph above had two cells, each labelled ‘1.2 V’, what
would the total voltage be?

152 10 Electricity

A+E