New
New
Length of a wire
I can explain why longer wires have a higher resistance than shorter wires.
Lesson 3 of 9
New
New
- Year 9
Length of a wire
I can explain why longer wires have a higher resistance than shorter wires.
Lesson details
Key learning points
- The longer a wire, the greater its resistance.
- Electric current in a wire is a flow of electrons moving through the spaces between ‘atoms’ (metal ions).
- Doubling the length of a wire doubles its resistance.
- Doubling the length of a wire doubles the number of ‘atoms’ (metal ions) in the way of the flow of electrons.
- The resistance of a (uniform) wire is proportional to its length.
Keywords
Resistance - Resistance is a measure of how hard it is for current to flow.
Metal ion - A metal ion is formed when a metal atom loses one or more electrons and has a positive charge.
Electron - Electrons are the charges in conductors that flow to give an electric current.
Proportional - Two variables are proportional if one changes as a multiple of the other.
Common misconception
Many pupils are likely to still use the terms current, voltage and resistance interchangeably.
Repeatedly question pupils about each term and challenge them to use each one correctly throughout their explanations, both written and verbal.
Ensure there are clear explanations to explain what current, voltage and resistance are to pupils and encourage pupils to use correct terminology and explanations as frequently as they can. When using models, ensure that pupils know the limitations of the models and that they are not the reality.
Teacher tip
Equipment
Constantan, or nichrome wire, SWG 30-40, metre rules, crocodile clips, electrical leads, ammeters capable of measuring current in milliamps, 3V batteries, wire cutters.
Content guidance
- Risk assessment required - equipment
Supervision
Adult supervision required
Licence
This content is © Oak National Academy Limited (2026), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).
Lesson video
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Prior knowledge starter quiz
6 Questions
Q1.Which of the following particles are the moving charges in a metal?
Which of the following particles are the moving charges in a metal?
protons
neutrons
gravitons
Correct answer: electrons
electrons
Q2.Which of the following statements explain what happens if a bare copper wire is folded in half and doubled back on itself?
Which of the following statements explain what happens if a bare copper wire is folded in half and doubled back on itself?
Correct answer: The cross–sectional area doubles.
The cross–sectional area doubles.
The cross–sectional area halves.
Correct answer: The current it can carry will double.
The current it can carry will double.
Its resistance will double.
Q3.Which of the following statements explain what we mean when we say two variables are proportional?
Which of the following statements explain what we mean when we say two variables are proportional?
Correct answer: One variable changes as a multiple of the other one.
One variable changes as a multiple of the other one.
If one variable increases, the other one decreases.
If one variable increases, the other one remains constant.
Both variables stay the same if the other one changes.
Q4.Which of the following statements describe the role of the plastic insulation around the copper wires in the cable shown?
Which of the following statements describe the role of the plastic insulation around the copper wires in the cable shown?
Correct answer: To stop the metal wires touching each other.
To stop the metal wires touching each other.
Correct answer: To protect us from electrical shocks.
To protect us from electrical shocks.
Correct answer: To help us identify the wires.
To help us identify the wires.
To make the wires look nicer.
Q5.The two wires shown are made from the same material.
Which of the following resistances is the resistance of the thin wire?
The two wires shown are made from the same material.
Which of the following resistances is the resistance of the thin wire?
$${1\over2} \Omega$$
1 $$\Omega$$
4 $$\Omega$$
Correct answer: 8 $$\Omega$$
8 $$\Omega$$
Q6.A wire with a cross–sectional area of 1 mm$$^2$$ allows a current of 0.2 A to flow through it.
What current will flow in a wire of the same material with a cross–sectional area of 4 mm$$^2$$?
A wire with a cross–sectional area of 1 mm$$^2$$ allows a current of 0.2 A to flow through it.
What current will flow in a wire of the same material with a cross–sectional area of 4 mm$$^2$$?
0.2 A
0.4 A
Correct answer: 0.8 A
0.8 A
1.6 A
Assessment exit quiz
6 Questions
Q1.Which of the following statements describes the cause of resistance in metal wires?
Which of the following statements describes the cause of resistance in metal wires?
Electrons in the wire repel each other.
Electrons in the wire are attracted by atoms.
Correct answer: Electrons in the wire collide with metal ions.
Electrons in the wire collide with metal ions.
Electrons in the wire collide with the sides of the wire.
Q2.The image shown is a representation of the arrangment of the particles in a metal.
Which of the following particles do the black spheres represent?
The image shown is a representation of the arrangment of the particles in a metal.
Which of the following particles do the black spheres represent?
electrons
protons
neutrons
Correct answer: metal ions
metal ions
Q3.A metal wire has a resistance of 6 $$\Omega$$.
Which of the following resistances is the new resistance of the wire if its length is increased by three times?
A metal wire has a resistance of 6 $$\Omega$$.
Which of the following resistances is the new resistance of the wire if its length is increased by three times?
2 $$\Omega$$
3 $$\Omega$$
6 $$\Omega$$
12 $$\Omega$$
Correct answer: 18 $$\Omega$$
18 $$\Omega$$
Q4.Which of the following resistances is the total resistance of the combination of resistors shown?
Which of the following resistances is the total resistance of the combination of resistors shown?
1 $$\Omega$$
2 $$\Omega$$
3 $$\Omega$$
4 $$\Omega$$
Correct answer: 7 $$\Omega$$
7 $$\Omega$$
Q5.A current of 0.4 A flows through a resistance cable which is 12 m long.
What current will flow through 3 m of the same resistance cable?
A current of 0.4 A flows through a resistance cable which is 12 m long.
What current will flow through 3 m of the same resistance cable?
0.1 A
0.2 A
0.4 A
0.8 A
Correct answer: 1.6 A
1.6 A
Q6.The cross–sectional area of a wire is doubled and the length is halved.
Which of the following statements describes what will happen to the resistance of the wire?
The cross–sectional area of a wire is doubled and the length is halved.
Which of the following statements describes what will happen to the resistance of the wire?
The resistance halves.
Correct answer: The resistance stays the same.
The resistance stays the same.
The resistance doubles.
The resistance increases by a factor of four.
