Basic Magnetism

Objectives

Lesson outcomes

Describe attraction and repulsion between magnetic poles and between magnets and magnetic materials.
Explain induced magnetism and compare temporary magnets with permanent magnets.
Draw and interpret magnetic field lines around a bar magnet and use them to show field direction.
Explain how field-line spacing shows field strength.

Syllabus

CIE 0625 syllabus points

11 linked

4.1.1 Describe the forces between magnetic poles and between magnets and magnetic materials, including the use of the terms north pole (N pole), south pole (S pole), attraction and repulsion, magnetised and unmagnetised
4.1.2 Describe induced magnetism
4.1.3 State the differences between the properties of temporary magnets (made of soft iron) and the properties of permanent magnets (made of steel)
4.1.4 State the difference between magnetic and non-magnetic materials
4.1.5 Describe a magnetic field as a region in which a magnetic pole experiences a force
4.1.6 Draw the pattern and direction of magnetic field lines around a bar magnet
4.1.7 State that the direction of a magnetic field at a point is the direction of the force on the N pole of a magnet at that point
4.1.8 Describe the plotting of magnetic field lines with a compass or iron filings and the use of a compass to determine the direction of the magnetic field
4.1.9 Describe the uses of permanent magnets and electromagnets
4.1.10 Explain that magnetic forces are due to interactions between magnetic fields
4.1.11 Know that the relative strength of a magnetic field is represented by the spacing of the magnetic field lines

Definitions

Required definitions

Magnetic field
a region where a magnetic pole experiences a force.

Lesson Notes

Student guidance and lesson notes

Overview

This lesson gives you the language and diagrams for the rest of electromagnetism. If you can already describe poles, magnetic materials, induced magnetism, and field lines clearly, the later lessons on electromagnets, motors, and generators will make much more sense.

What You Need to Know

Like poles repel and unlike poles attract.
Magnets also attract magnetic materials such as iron and steel, but non-magnetic materials do not respond in the same way.
Induced magnetism happens when a magnetic material becomes magnetised by being placed in a magnetic field.
Soft iron is useful for temporary magnets because it magnetises easily and loses magnetism quickly. Steel is useful for permanent magnets because it keeps its magnetism.
Use the magnetic field idea to explain why field-line diagrams can predict forces on poles.
Magnetic field lines show the shape and direction of the field. Outside a bar magnet, they go from north to south.
Field lines that are closer together show a stronger field.

How to Work Through It

Start by classifying examples into magnetic and non-magnetic materials.
Practise describing what happens when different poles are brought together.
Draw field lines around a bar magnet and use a plotting compass to decide the correct direction.
Compare temporary and permanent magnets so you can link their properties to real uses.

Check Your Understanding

What is the difference between attraction to a magnetic material and attraction between two poles?
Why is soft iron better for a temporary magnet than steel?
In which direction do field lines point around a bar magnet?
What does it mean if the field lines are very close together in one region?

Common Mistakes

Thinking all metals are magnetic. Only some materials, such as iron and steel, are magnetic.
Forgetting that field direction is defined by the force on a north pole.
Drawing field lines crossing each other. A magnetic field at one point can only have one direction.

Next Steps

Use the slides to practise field-line diagrams until you can sketch them without guessing.
Keep the ideas of direction and field strength secure because they will be used again in current and motor-effect lessons.