Page 157 - Science Coursebook

10.8 Changing circuits 2

Activity 10.8A
Variable resistors

SE Your teacher will show you how a variable resistor can be
used to change the current in a circuit.
1 Draw a circuit diagram to represent this circuit.
2 Write a sentence to describe what you
observe as the variable resistor is altered. Moving the slider along
3 Write another sentence to explain what changes the resistance variable resistor
you observe. in the circuit.

Activity 10.8B

Make your own variable resistor

SE In the circuit shown, two clips connect to a length
of resistance wire.

Construct the circuit and observe what happens
when you slide the clips along the wire so that
they are closer together or farther apart.
Try to explain what you observe. Resistance wire has more resistance wire
resistance than normal wire.

Losing energy
When two components are connected in series in a circuit, it is harder for the current to

flow. There is more resistance, and so the current is smaller.
It requires energy for the electrons to flow through any component which has resistance.

That’s not a bad thing! We want the current to transfer energy to a buzzer so that it will
make a sound or a lamp so that it will give out light.

Question
2 a Draw a circuit diagram to show a circuit with two cells and two resistors
connected in series. Include an ammeter to measure the current in the circuit.
b Add arrows to show how the electric current flows around the circuit.

c Explain why the current in the circuit would be bigger if there was only one
resistor in the circuit.

Summary
• Components with resistance make the current in a circuit smaller.
• When components are connected in series, the resistance in the circuit
is greater and so the current is smaller.

10 Electricity 155