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Unit 9: Magnetism and electromagnets

Electromagnets — HIA International - Grade 7 Revision Notes & Topical Questions

5 min read 7 parts Lesson 4 of 5 2 quizzes

📚 HIA International - Grade 7 Hub / Topical Revision
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Lesson summary

Electromagnets — HIA INTERNATIONAL notes: Describe how an electromagnet is made, how its poles are found and reversed, and its uses.Magnetic material — a material attracted to a magnet, such as iron, nickel, cobalt and steel.Steel — a common magnetic metal that is a mixture conta…

  • Magnetised
  • Permanent magnet
  • Current on
  • Current off
  • Finding the poles
  • Reversing the poles

Section 1 of 7Magnetic materials and magnetising

Magnetic material
  • Magnetic material a material attracted to a magnet, such as iron, nickel, cobalt and steel.
Steel
  • Steel a common magnetic metal that is a mixture containing a large proportion of iron.
Magnetised
Magnetised turned into a magnet.
Permanent magnet
  • Permanent magnet has a magnetic field that is always there and cannot be switched off.
Electromagnet
  • Electromagnet a magnet made by magnetising a material using electricity.

Section 2 of 7Making an electromagnet

Coil
  • Coil wire is wrapped around a magnetic material, and the wire wrapped around is called the coil.
Core
  • Core the material in the middle of the coil is called the core, e.g. an iron nail.
Current on
  • Current on when current passes through the coil, the core becomes magnetised.
Current off
  • Current off the core loses most of its magnetism when the current is switched off.
1
Wrap insulated wire tightly around an iron nail to form a coil.
2
Leave enough wire at each end to connect to the cell.
3
Connect the coil to a cell and switch.
4
Switch on briefly and test the nail with paper clips.
Making an electromagnet
Only the plastic coating of the wire should touch the nail.
Switch on for the shortest time, or the cell will not last.

Section 3 of 7Poles of an electromagnet

Two poles
  • Two poles an electromagnet has a north and a south pole, like a bar magnet.
Finding the poles
  • Finding the poles use a compass or a bar magnet with known poles.
  • A compass points along the field lines, so it points towards the south pole.
  • Opposite poles attract and like poles repel, so a bar magnet shows which pole is which.
Reversing the poles
  • Reversing the poles wrap the coil in the opposite direction, or reverse the connections to the cell or power supply.
  • The same happens when the current is reversed.

Section 4 of 7Uses of electromagnets

UseHow the electromagnet is used
Fire doorHolds the door open; the alarm switches it off and the door closes
MRI scannerPowerful electromagnets make images inside the human body
Scrap metal sortingLifts iron and steel but not copper, aluminium or zinc, and drops them when switched off
ToasterHolds the basket down until a timer switches it off and the toast pops up
Electric bellPulls the hammer to the bell, breaking the circuit; the hammer springs back and the cycle repeats
Electric motorChanges electrical energy into kinetic energy

Section 5 of 7Electromagnet or permanent magnet

FeatureElectromagnetPermanent magnet
MagnetismOnly while current flowsAlways present
SwitchingCan be switched on and offCannot be switched off
StrengthCan be changedFixed
PolesCan be reversedCannot be reversed

Section 6 of 7Key terms

TermMeaning
ElectromagnetA magnet made by passing an electric current through a coil of wire around a magnetic core.
CoilThe wire wrapped around the core of an electromagnet.
CoreThe magnetic material in the middle of a coil.
Permanent magnetA magnet whose magnetic field is always there.
MagnetisedTurned into a magnet.
Magnetic materialA material attracted to a magnet, such as iron, steel, nickel or cobalt.

Section 7 of 7Exam technique

1
Magnetic and magnetised mean the same — a magnetic material is attracted to magnets, magnetised means it has been turned into a magnet.
2
An electromagnet is magnetic all the time — it is magnetic only while current flows.
3
Copper and aluminium can be lifted by an electromagnet — only magnetic metals such as iron and steel can.
4
Wire used in a coil needs no insulation — only the insulating coating keeps current in the coil and off the core.

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