Resistance of a wire at a constant temperature | Combined science

Starter quiz

Match the following quantities to its unit symbol.

potential difference

⇔

V ✓

resistance

⇔

Ω ✓

current

⇔

A ✓
Which of the following can be used to calculate resistance?

charge ÷ potential difference

current × potential difference

current ÷ potential difference

potential difference × charge

potential difference ÷ current ✓
Match each of the following types of variable to its definition.

control variable

⇔

a variable that needs to be kept the same in a fair test ✓

dependent variable

⇔

the variable that is measured to get a set of results ✓

independent variable

⇔

the variable that the experimenter selects values for ✓
When a current flows in a wire, which of the following moves through the wire?

atoms

electrons ✓

ions

protons
In a graph showing the results of an experiment, where does each type of variable usually appear?

dependent variable

⇔

$y$ -axis ✓

control variable

⇔

does not appear on the graph ✓

independent variable

⇔

$x$ -axis ✓
When there is an error in an experimental measurement, which of the following must be true?

The measurement is anomalous.

The measured value is different from the true value. ✓

The experimenter did not follow the method correctly.

Exit quiz

A type of error that can affect results in an unpredictable way is called a ______ error.

'random' ✓
A pupil investigates the relationship between the length of a wire and the resistance of the wire. Which of the following are control variables in this investigation?

the length of the wire

the material of the wire ✓

the thickness of the wire ✓

the temperature of the wire ✓

whether the wire is straight or coiled
Which of the following statements describes how to connect a voltmeter and ammeter to measure the resistance of a piece of wire in a circuit?

Connect a voltmeter in series and an ammeter in parallel with the wire.

Connect a voltmeter in parallel and an ammeter in series with the wire. ✓

Connect both a voltmeter and an ammeter in series with the wire.

Connect both a voltmeter and an ammeter in parallel with the wire.
The diagram shows some of the apparatus for investigating the effect of length of a wire on its resistance. Which of the following will help keep the temperature of the wire constant?

use hot water

replace the water between measurements ✓

stir the water before taking a measurement ✓

take the thermometer out of the water between measurements
Which of the following increase the resistance of a metal wire?

increasing the length of the wire ✓

increasing the temperature of the wire ✓

increasing the cross-sectional area of the wire

making the wire curved instead of straight
Sort the following sentences into the correct order to explain why the resistance of a wire may increase when a current flows in it.

1

⇔

Electrons move through the wire.

2

⇔

As they do, they collide with metal ions.

3

⇔

This makes the ions move more (so the temperature of the wire increases).

4

⇔

This makes collisions happen more often.

5

⇔

So it is harder for electrons to flow – the resistance is greater.

Worksheet

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Lesson Details

Key learning points

A wire heats up when a current flows and its temperature will vary over time.
A water bath helps to keep the temperature of a wire constant.
Turning a circuit on for a very short time reduces the heating effect in a wire.
In electricity investigations, it is often easy to take lots of readings rather than a few, repeated readings.
The resistance of a wire is directly proportional to its length, at a constant temperature.

Common misconception

Pupils may not realise that the resistance of a wire varies with temperature.

Ensure pupils are aware that the temperature of a metal wire does affect resistance and that precautions should be taken to avoid a temperature change.

Keywords

Independent variable - the variable that the person doing the experiment changes
Dependent variable - the variable that is measured; it changes as a result of varying the independent variable
Control variable - a variable that needs to be kept the same to allow a fair test to be carried out
Random error - a type of error that affects results in an unpredictable way
Directly proportional - describes the relationship between two variables if both increase in the same proportion as each other