New
New
Year 10
OCR
Higher

Resistance of a wire at a constant temperature

I can describe how to investigate the resistance of a wire at a constant temperature and make scientific conclusions.

New
New
Year 10
OCR
Higher

Resistance of a wire at a constant temperature

I can describe how to investigate the resistance of a wire at a constant temperature and make scientific conclusions.

Lesson details

Key learning points

  1. A wire heats up when a current flows and its temperature will vary over time.
  2. A water bath helps to keep the temperature of a wire constant.
  3. Turning a circuit on for a very short time reduces the heating effect in a wire.
  4. In electricity investigations, it is often easy to take lots of readings rather than a few, repeated readings.
  5. 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

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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6 Questions

Q1.
Match the following quantities to its unit symbol.
Correct Answer:potential difference,V

V

Correct Answer:resistance,Ω

Ω

Correct Answer:current,A

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.

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?
An image in a quiz
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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