Page 155 - Science Coursebook

10.7 Changing circuits 1

Activity 10.7
Combining cells

SE Your task is to find out how the voltage of the cells in a circuit affects the current
in the circuit.
1 Set up a circuit with a cell, a switch and a lamp. Add an ammeter to measure
the current. Add a voltmeter to measure the voltage of the cell.
2 Ask your teacher to check your circuit before you close the switch.
3 Close the switch to complete the circuit. Record the values of the current
and the voltage.
4 Repeat the experiment using two cells, and then three cells. What pattern can
you see?
5 Repeat the whole experiment with a resistor in the circuit instead of the
lamp. Do you find the same pattern?

More volts, more amps
The activity shows that, if the cells in a circuit are providing a bigger voltage, the
current will also be bigger. This is because, if there are two cells connected in series,
they give a bigger push to the electrons in the wires, so there is a bigger current.
If there is a bigger current, the lamp will shine more brightly. The current is
transferring energy more quickly from the cells to the lamp.

Question

A+I 4 Study the circuits in the diagram. Each circuit will have a different current
flowing in it. Put them in order, starting with the one with the biggest current.

(All the cells have the same voltage.)
+ − + − − + + − + − + −

A B C

Summary
• A voltmeter is used to measure the voltage of a cell.
• When two or more cells are connected positive to negative in series,
their voltages add up.
• A bigger voltage in a circuit makes a bigger current flow.

10 Electricity 153