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Year 9

Current through an electromagnet

I can plan an experiment to test the strength of an electromagnet and explain how different factors affect the strength of an electromagnet.

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New
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Year 9

Current through an electromagnet

I can plan an experiment to test the strength of an electromagnet and explain how different factors affect the strength of an electromagnet.

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Share activities with pupils
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Lesson details

Key learning points

  1. The more turns of wire in the coil of an electromagnet, the stronger its magnetic field.
  2. The greater the current through the coil of an electromagnet, the stronger its magnetic field.
  3. The more closely spaced the coils of wire of an electromagnet, the stronger its magnetic field.
  4. An electromagnet made from bare wire will not work if adjacent turns are touching.
  5. A soft iron core increases the strength of an electromagnet because it becomes magnetised when it is turned on.

Keywords

  • Independent variable - the variable that the person doing the experiment changes

  • Dependent variable - the variable that the person doing the experiment measures

  • Control variable - the variables that may affect the dependent variable and should be kept the same

  • Fair test - an experiment where the control variables are kept the same

  • Soft iron core - the centre of a strong electromagnet that becomes magnetised

Common misconception

Pupils often refer to the turns of a coil as the number of coils.

Emphasise that turns of wire can be added to a coil to make the coil longer.

Using a power pack, to control the size of a current through an electromagnet, can easily cause excessive heating of wires. Either demonstrate the effect of current, or test electromagnets with a battery of 0, 1, 2 and 3 × 1.5 V cells in series in order to test different currents.
Teacher tip

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).

Lesson video

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Starter quiz

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6 Questions

Q1.
Which of the following statements about an object made of a magnetic material are correct?
Correct answer: It could be used to make a magnet.
It has a north–seeking pole and a south–seeking pole.
It is attracted to all other objects made of magnetic material.
Correct answer: It experiences a force when there is a magnet nearby.
Q2.
A pupil moves two pieces of metal towards each other and they attract each other by a magnetic force. Which of the following statements are correct?
Correct answer: Both pieces could be magnets.
Correct answer: One piece could be a magnet and not the other.
Neither piece could be a magnet.
Correct answer: Both pieces must be made of a magnetic material.
Q3.
A pupil moves two pieces of metal towards each other and they repel each other by a magnetic force. Which of the following statements are correct?
Correct answer: Both pieces are magnets.
Only one piece is a magnet.
Neither piece is a magnet.
Correct answer: Both pieces are made of magnetic material.
Q4.
An electromagnet has a coil of wire wrapped around an iron core. A current flows in the wire. Which of the following statements explains why the electromagnet behaves like a magnet?
A magnet is used to make the core.
The wires are made of a magnetic material.
Correct answer: There is a magnetic field around the current–carrying wire.
The wire gets hot, which heats the core and makes it magnetic.
Q5.
Which of the following would decrease the strength of an electromagnet’s magnetic field?
Correct answer: reducing the current in the coil
reducing the resistance of the coil
increasing the number of turns (loops) in the coil
Correct answer: replacing the iron core with a wooden core
Q6.
Which of the following statements are correct?
Correct answer: An electromagnet can attract a magnet.
Correct answer: An electromagnet can repel another electromagnet.
Only one end of an electromagnet can pick up iron paperclips.

Exit quiz

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6 Questions

Q1.
Match the following key terms to their definition.
Correct Answer:dependent variable,The variable that is measured by a person doing an experiment.

The variable that is measured by a person doing an experiment.

Correct Answer:control variable,A variable that is kept the same by a person doing an experiment.

A variable that is kept the same by a person doing an experiment.

Correct Answer:independent variable,The variable that is changed by a person doing an experiment.

The variable that is changed by a person doing an experiment.

Q2.
Which of the following statements describes a fair test?
An experiment that has an independent variable.
An experiment that gives accurate and reliable results.
An experiment that gives the same results each time it is repeated.
Correct answer: An experiment in which the experimenter changes only one variable.
Q3.
A pupil tests how the strength of an electromagnet’s magnetic field is affected by the current in its coil. What is the independent variable in this experiment?
Correct answer: current in the coil
number of turns in the coil
strength of the magnetic field
material the core is made from
number of paperclips the electromagnet can pick up
Q4.
A pupil tests how the strength of an electromagnet’s magnetic field is affected by the current in the coil. Which of the following are control variables in this experiment?
strength of the magnetic field
current in the coil
Correct answer: number of turns in the coil
Correct answer: material the core is made from
number of paperclips the electromagnet can pick up
Q5.
Electromagnets typically have a core made of pure iron inside the coil, known as a soft iron core. What does ‘soft’ mean when describing the iron core?
The iron is easy to bend.
The iron is hard to bend.
The iron remains magnetised after the current is switched off.
Correct answer: The iron becomes demagnetised after the current is switched off.
Q6.
A pupil wants to make an electromagnet. They wrap bare wire around an iron core and pass a current through the wire. Why does their electromagnet not work?
Correct answer: It has a very weak magnetic field.
The coils are repelled by the core.
The coils of wire melt and stick to the core.
Correct answer: Current does not go around the turns of the coil.