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
English | Russian | Kazakh |
Soft magnetic materials | ||
Hard magnetic materials | ||
Paramagnetic | ||
Ferromagnetic | ||
Diamagnetic | ||
Magnetic materials | ||
magnetization |
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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: 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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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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Magnets and Magnetic Materials
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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Quantifying Magnetic Properties
Quantity | Symbol | SI Units |
Field | H | A/m |
Flux Density | B | tesla |
Flux | Φ | weber |
Magnetization | M | A/m |
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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
Like poles repel unlike poles attract.
The closer the poles, the greater the force between them.
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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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Arrangement of blocks | Effect |
A near B | attraction |
B near C | |
A near C | No effect |
B near D |
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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Fill in the gaps below:
Magnetic materials are either hard or ______. Hard magnetic materials such as ______ retain their magnetisation once magnetised.
A magnetic _____ is a region where the magnetic force is greatest. Magnetic poles always occur in ______. Like poles _______, unlike attract.
A magnetic ______ is a region where magnetic force is exerted. The ________ of the magnetic field around a bar magnet is from north to south.
soft
repel
field
steel
direction
pole
pairs
WORD SELECTION:
soft
repel
field
steel
direction
pole
pairs
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Complete the table
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Material | Magnetic Field | Magnetic Force | Permeability |
Ferromagnetic | |||
Paramagnetic | |||
Diamagnetic |
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