By changing the length of a piece of wire, the resistance of electrical circuits will be investigated. This is done by measuring the potential difference and current across a circuit with a varying length of thin resistance wire at a constant temperature and finding the resistance using Ohm's law.

Equations

Word equation	symbol equation
$potential \space difference = current \times resistance$	$V = I \times R$

Variable definitions

quantity name	Symbol	unit name	unit symbol
$potential \space difference$	$V$	$volt$	$V$
$current$	$I$	$ampere$	$I$
$resistance$	$R$	$ohm$	$\Omega$

Equipment list

The following equipment list can be used to conduct the experiment to investigate resistance.

Equipment	Use
Digital ammeter	To measure the current in the circuit.
Digital voltmeter	To measure the potential difference across components.
Thin resistance wire	To measure the resistance of.
Crocodile clips	To attach to the length of wire.
Connecting leads	To connect each element of the circuit together.
Battery or suitable power supply	To provide power to the circuit.
Metre ruler	To measure the length of the resistance wire.

Experimental variables

The independent variable is the variable you change. The dependent variable is the variable that changes depending on the other variables and is the one you measure. The control variables are the variables that are kept constant.

Independent variable	$Length\ of\ the\ wire,\ L$
Dependent variable	$Resistance,\ R$
Control variable	$Potential\ difference\ of\ power\ supply,\ temperature\ of\ the\ wire$

Safety precautions

When performing experiments, it is very important to consider safety precautions. This is so that no one gets hurt or injured during the experiment.

Hazard

risk

Safety measure

Hot wires

The resistance can cause the wires used in the circuit to heat up. These can cause burns if touched.

Do not touch the wires directly if the circuit is switched on or has just recently been turned off. Switch off the power supply if burning can be smelled.

If burnt, run the burn under cold water for five minutes.

Liquids spilled onto circuit

Liquids can damage the electrical equipment and may cause a fire.

Make sure there are no liquids close to the electrical equipment.

Method

These are the instructions to complete the experiment. Record all measurements taken as you work through the experiment in a table.

Physics; Physics practicals; KS4 Year 10; Investigating the resistance of a length of wire

A.	Ammeter
B.	Power supply
C.	Voltmeter
D.	Crocodile clips
E.	Thin resistance wire
F.	Ruler

1.	Set up the apparatus as shown in the diagram. Attach one crocodile clip to the start of the ruler and the other at the $10\,cm$ mark. Set the power supply to $1.5\,V$ . Tip: Make sure that the first crocodile clip is attached exactly at $0\,cm$ to prevent a zero error (systematic error from not starting exactly at zero).
2.	Record the readings from the voltmeter and ammeter.
3.	Move the second crocodile clip $10\,cm$ further away and take new readings of the voltmeter and ammeter. Note: The power supply should be turned off between readings and whilst moving the crocodile clip.
4.	Repeat step 3 for more measurements until the second crocodile clip reaches the end of the ruler.

Analysis

This is how you will use the data recorded to form conclusions.

1.	Calculate the value of resistance, $R$ , for each length of wire using a rearranged form of the Ohm's law equation: $V = I \times R \to R = \dfrac{V}{I}$
2.	Plot a graph of resistance, $R$ ( $y$ -axis) against the length of wire, $L$ ( $x$ -axis). Draw a line of best fit.

Conclusion

The graph should look like this and have a positive correlation with the line of best fit going through the origin. The results of this graph conclude that the longer the length of wire, the higher the resistance across it. Therefore, resistance is directly proportional to the length of the wire.

Evaluation

Once you have completed your experiment, it is important to consider how it could be improved. You should come up with ways to improve the accuracy of your values. If you got a result that seems unreasonable, think about why this was.

Learn with Basics

Length:

Unit 1

Measuring current and potential difference

Unit 2

Potential difference and resistance

Jump Ahead

Optional

Unit 3

Investigating the resistance of a length of wire

Final Test

Create an account to complete the exercises

FAQs - Frequently Asked Questions

What does the graph of length against resistance for a wire look like?

The graph is a straight line through the origin.

How can you find the resistance of a length of wire?

You can find the resistance by measuring the potential difference and current across a circuit with a varying length of thin resistance wire at a constant temperature and finding the resistance using Ohm's law.

How does the length of a wire affect resistance?

The longer the length of wire, the higher the resistance across it. Therefore, resistance is directly proportional to the length of the wire.

Home

Physics

Physics practicals

Investigating the resistance of a length of wire

Videos

Summary

Exercises

Select Lesson

Exam Board

Select an option

Physics practicals

Matter

Calculating density

States of matter and changes of state

Specific heat capacity

Specific latent heat

Temperature and pressure of gases

Elasticity and the spring constant

Magnetic fields

Magnetism and magnetic fields

Electromagnetism and solenoids

Motor effect and electromagnetic induction - Higher

Transformers

Electricity and circuits

Forces and energy

Energy stores and systems

Calculating work done and power

Forces and vector diagrams

Radioactivity

The structure of the atom

Electron energy levels and ionisation

Isotopes and radioactive decay

Half-life and calculating radioactive decay

Irradiation and contamination

Waves and the electromagnetic spectrum

Waves: properties, types and equations

Refraction and ray diagrams

The electromagnetic spectrum

Uses of electromagnetic waves

Conservation of energy

Energy stores and transfers

Mechanical energy stores

Conduction and convection

Energy efficiency

Renewable and non-renewable resources

Motion and forces

Working scientifically

Practical skills

Measuring techniques

Safety and ethics

Designing experiments

Methods of heating substances

Working with electronics

Random sampling and sampling methods

Comparing results using percentage change

Explainer Video

Tutor: Madeleine

Summary

Investigating the resistance of a length of wire

In a nutshell

Equations

Word equation	symbol equation
$potential \space difference = current \times resistance$	$V = I \times R$

Variable definitions

quantity name	Symbol	unit name	unit symbol
$potential \space difference$	$V$	$volt$	$V$
$current$	$I$	$ampere$	$I$
$resistance$	$R$	$ohm$	$\Omega$

Equipment list

The following equipment list can be used to conduct the experiment to investigate resistance.

Equipment	Use
Digital ammeter	To measure the current in the circuit.
Digital voltmeter	To measure the potential difference across components.
Thin resistance wire	To measure the resistance of.
Crocodile clips	To attach to the length of wire.
Connecting leads	To connect each element of the circuit together.
Battery or suitable power supply	To provide power to the circuit.
Metre ruler	To measure the length of the resistance wire.

Experimental variables

Independent variable	$Length\ of\ the\ wire,\ L$
Dependent variable	$Resistance,\ R$
Control variable	$Potential\ difference\ of\ power\ supply,\ temperature\ of\ the\ wire$

Safety precautions

When performing experiments, it is very important to consider safety precautions. This is so that no one gets hurt or injured during the experiment.

Hazard

risk

Safety measure

Hot wires

The resistance can cause the wires used in the circuit to heat up. These can cause burns if touched.

Do not touch the wires directly if the circuit is switched on or has just recently been turned off. Switch off the power supply if burning can be smelled.

If burnt, run the burn under cold water for five minutes.

Liquids spilled onto circuit

Liquids can damage the electrical equipment and may cause a fire.

Make sure there are no liquids close to the electrical equipment.

Method

These are the instructions to complete the experiment. Record all measurements taken as you work through the experiment in a table.

A.	Ammeter
B.	Power supply
C.	Voltmeter
D.	Crocodile clips
E.	Thin resistance wire
F.	Ruler

1.	Set up the apparatus as shown in the diagram. Attach one crocodile clip to the start of the ruler and the other at the $10\,cm$ mark. Set the power supply to $1.5\,V$ . Tip: Make sure that the first crocodile clip is attached exactly at $0\,cm$ to prevent a zero error (systematic error from not starting exactly at zero).
2.	Record the readings from the voltmeter and ammeter.
3.	Move the second crocodile clip $10\,cm$ further away and take new readings of the voltmeter and ammeter. Note: The power supply should be turned off between readings and whilst moving the crocodile clip.
4.	Repeat step 3 for more measurements until the second crocodile clip reaches the end of the ruler.

Analysis

This is how you will use the data recorded to form conclusions.

1.	Calculate the value of resistance, $R$ , for each length of wire using a rearranged form of the Ohm's law equation: $V = I \times R \to R = \dfrac{V}{I}$
2.	Plot a graph of resistance, $R$ ( $y$ -axis) against the length of wire, $L$ ( $x$ -axis). Draw a line of best fit.

Conclusion

Evaluation

Learn with Basics

Length:

Unit 1

Measuring current and potential difference

Unit 2

Potential difference and resistance

Jump Ahead

Optional

Unit 3

Investigating the resistance of a length of wire

Final Test

Create an account to complete the exercises

FAQs - Frequently Asked Questions

What does the graph of length against resistance for a wire look like?

The graph is a straight line through the origin.

How can you find the resistance of a length of wire?

How does the length of a wire affect resistance?

The longer the length of wire, the higher the resistance across it. Therefore, resistance is directly proportional to the length of the wire.

Investigating the resistance of a length of wire

Videos

Summary

Exercises

Select Lesson

Exam Board

Physics practicals

Matter

Magnetic fields

Electricity and circuits

Forces and energy

Radioactivity

Waves and the electromagnetic spectrum

Conservation of energy

Motion and forces

Working scientifically

Practical skills

Explainer Video

Summary

Investigating the resistance of a length of wire

​​In a nutshell

​​Word equation

symbol equation

quantity name

​​Symbol

​​unit name

​​unit symbol

​​Equipment

Use

Experimental variables

Safety precautions

​​Hazard

risk

Safety measure

Method

Analysis

Conclusion

Evaluation

Learn with Basics

Unit 1

Measuring current and potential difference

Unit 2

Potential difference and resistance

Jump Ahead

Unit 3

Investigating the resistance of a length of wire

Final Test

FAQs - Frequently Asked Questions

What does the graph of length against resistance for a wire look like?

How can you find the resistance of a length of wire?

How does the length of a wire affect resistance?

Investigating the resistance of a length of wire

Videos

Summary

Exercises

Select Lesson

Exam Board

Physics practicals

Matter

Magnetic fields

Electricity and circuits

Forces and energy

Radioactivity

Waves and the electromagnetic spectrum

Conservation of energy

Motion and forces

Working scientifically

Practical skills

Explainer Video

Summary

Investigating the resistance of a length of wire

​​In a nutshell

​​Word equation

symbol equation

quantity name

​​Symbol

​​unit name

​​unit symbol

​​Equipment

Use

In a nutshell

Word equation

Symbol

unit name

unit symbol

Equipment

Hazard

In a nutshell

Word equation

Symbol

unit name

unit symbol

Equipment

Hazard