57.58_Magnetic Properties of Materials

Lesson Objectives

By the end of the lesson learners will be able:

10.4.1.3 – to describe modern scopes of using magnetic substances (neodymium magnets, sensors, seismographs, metal detectors) and to discuss the tendency of their application;

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Keywords

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Types of Magnetic Materials

Magnetic: Can be magnetized and are attracted to magnets

Non-magnetic: Cannot be magnetized e.g. brass, copper, zinc, tin, aluminium, non-metals

Ferromagnetic: Strongly attracted by a magnetic field: iron, nickel, cobalt

Paramagnetic: Slightly attracted by a magnetic field: magnesium, molybdenum, lithium, tantalum

Diamagnetic: slightly repelled by a magnetic field: copper, silver, gold

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Explain these terms

Field:

Magnetic Flux Density:

Magnetic Flux:

Magnetization:

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Explain these terms

Field: Region where magnetism is experienced

Magnetic Flux Density: Number of magnetic lines of force cutting through a plane of given area at right angle.

Magnetic Flux: Total number of lines of magnetic force in a material

Magnetization: Is a measure of the extent to which an object is magnetized

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Activity 1

Where does Magnetism come from?

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Where does Magnetism come from?

Each electron in an atom has a magnetic effect as it spins and orbits the nucleus.
Magnetic effects of the electrons cancel out in many atoms, some no, and atoms act like tony magnets called dipoles.
In unmagnetised state , the atomic magnets point in random directions.
In a fully magnetized state, more and more atomic magnets line up with each other.
Billions of tiny atomic magnets act as one big magnet
= Domain Theory.

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Dipole Arrangements

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Magnets attract objects made of magnetic materials

Magnetic materials include the elements iron, nickel, cobalt,
alloys containing some of these such as steel and some of their compounds.

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More Sizes and Shapes

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Magnadur Magnets

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Quantifying Magnetic Properties

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Hard and Soft Magnetic Materials

Permanent magnets are made of magnetically HARD materials such as steel, alcomax, magnadur. These materials retain their magnetisation once magnetised. Hard to magnetise.

Magnetically SOFT materials, such as iron, mumetal lose their magnetisation easily. They suitable for temporary magnets such as electromagnets. Easy to magnetise.

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Magnetic Poles

Magnetic poles are the parts of a magnet that exert the greatest force.

Magnetic poles occur in pairs usually called north (N) and south (S)

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Why North and South Poles?

A magnet suspended so that it can rotate freely horizontally will eventually settle down with one pole facing north and the other south.

This pole pointing north is therefore called the ‘north seeking pole’, usually shortened to just ‘north pole’.

The magnet has been orientated by the Earth’s magnetic field.

A compass is an application of this effect.

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The Law of Magnets

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Task

A, B, C, and D are small blocks of different materials. The table below shows what happens when two of the blocks are placed near one another. Say whether the block is a magnet, a magnetic material or anon magnetic material.

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Properties of Magnets

Has a magnetic field around it
Has two opposite poles( N and S ) which exert forces on other magnets.
Will attract magnetic materials by inducing magnetism in them
Will exert little or no force on a non magnetic material.

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Magnetic Properties of Materials

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Complete the table

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Key Summary

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Explain the applications of:
Neodymium magnets
Sensors
Seismographs
Metal detectors

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