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.

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

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.

Use a switch to turn the current on and off quickly, so that the heating effect of the current is minimised. Also use a low current to minimise heating. Consider setting up a demonstration of a water bath method, and explain how to shorten the wire if necessary.

Teacher tip

Equipment

Nichrome wire, crocodile clips, electrical leads, metre ruler, voltmeter and ammeter.

Content guidance

Risk assessment required - equipment

Supervision

Adult supervision required

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

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Worksheet

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Starter quiz

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6 Questions

Q1.

Match the following quantities to its unit symbol.

Correct Answer:potential difference,V

Correct Answer:resistance,Ω

Correct Answer:current,A

Q2.

Which of the following can be used to calculate resistance?

charge ÷ potential difference

current × potential difference

current ÷ potential difference

potential difference × charge

Correct answer: potential difference ÷ current

Q3.

Match each of the following types of variable to its definition.

Correct Answer:control variable,a variable that needs to be kept the same in a fair test

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

Correct Answer:dependent variable,the variable that is measured to get a set of results

the variable that is measured to get a set of results

Correct Answer:independent variable,the variable that the experimenter selects values for

the variable that the experimenter selects values for

Q4.

When a current flows in a wire, which of the following moves through the wire?

atoms

Correct answer: electrons

ions

protons

Q5.

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

Correct Answer:dependent variable,$$y$$-axis

$$y$$-axis

Correct Answer:control variable,does not appear on the graph

does not appear on the graph

Correct Answer:independent variable,$$x$$-axis

$$x$$-axis

Q6.

When there is an error in an experimental measurement, which of the following must be true?

The measurement is anomalous.

Correct answer: The measured value is different from the true value.

The experimenter did not follow the method correctly.

Exit quiz

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6 Questions

Q1.

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

Correct Answer: random

Q2.

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

Correct answer: the material of the wire

Correct answer: the thickness of the wire

Correct answer: the temperature of the wire

whether the wire is straight or coiled

Q3.

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.

Correct answer: 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.

Q4.

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

Correct answer: replace the water between measurements

Correct answer: stir the water before taking a measurement

take the thermometer out of the water between measurements

Q5.

Which of the following increase the resistance of a metal wire?

Correct answer: increasing the length of the wire

Correct answer: increasing the temperature of the wire

increasing the cross-sectional area of the wire

making the wire curved instead of straight

Q6.

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.

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