BTEC NC - Electronic and Electrical Principles - Principles of Magnetism

8/2/2019 BTEC NC - Electronic and Electrical Principles - Principles of Magnetism

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Brendan Burr BTEC National Certificate in ElectronicsPrinciples of Magnetism

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Task 1

1.1a) Permanent MagnetsPermanent magnets can exert a magnetic

force on objects without an outsideinfluence. This is because the materialcontains a ferromagnetic metal such asiron ore or nickel.The magnetic field represented by apermanent magnet can be clearlyexampled by using the diagrams to theright.The iron shavings on the second imageform a pattern that resembles the shape

of the first diagram.It is visible that there is force that runsthe length of the magnet, and indicatesthat there are different polarities.

b) ElectromagnetsElectromagnets have a magnetic field, which isgenerated by the passing of current throughan appropriate material. The generatedmagnetic field is limited by the amount of

current that can pass through thematerial.The major difference between anelectromagnet and permanent magnets isthe controllability of the electromagnet. Bysupplying the electromagnet with a currentthe magnetism can be manipulated on andoff.

c) Current Carrying ConductorWhen a current passes through a metal thereis a magnetic field which forms around thematerial. This magnetic field can be clearlyexampled on the diagram to the right, wherethe current flow determines the rotation ofthe electromagnetic field.The direction of the field can be indicated byplacing a compass needle close to the

affected iron shavings.

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1.2a)

b)Mild Steel the typical B/H slope is relatively steep and begins tosuccumb to magnetic saturation at around 1.3(T)/500(A/m).Mu Metal - the typical B/H slope begins rather steep, howeverbuckles to magnetic saturation drastically at around 0.6(T)/300(A/m).Silicon Iron the curve for silicon iron rises to around 1.4(B). Themagnetic saturation begins to slow the magnetic flux densityincrease, as the magnetic field strength is also increased.

For all of the B/H curves the increase of the magnetic field strengthresults in the magnetic flux reaching a plateau.

Material Relative Permeability rMild Steel 200-800

Mu Metal 200-5000Silicon Iron 1000-5000

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Task 2

2.1 Principles of electromagnetic induction:

Electromagnetic induction is where an electrical current is produced

by varying the magnetic field around an electrical circuit.By moving a coil in and out of a magnetic field, a current is producedwhich can be indicated by using an ammeter. This theory is used toproduce an alternating voltage by moving the magnets magnetic fieldin and out of range of a coil.There are two laws which can be followed when working withelectromagnetic induction.Faradays Laws:

1. An EMF is induced in a circuit whenever the magnetic fluxlinking the circuit changes in magnitude.

2. The magnitude of the induced EMF in the circuit is directlyproportional to the rate of change of the magnetic flux linkingthe circuit.

Lenzs Law:1. The law states that the direction of the induced EMF is such

that it always opposes the change which produced it.

2.2 Two applications of electromagnetic induction:

Electrical Generator an electrical generator converts mechanicalenergy, into electrical energy. The form of mechanical energy can

come from many things, such as wind turbines, waterwheels or assimple as a hand crank. By having a consistent mechanical energysource it is possible to have a consistent electrical supply also. Onthis basis Green Energy is produced, where mechanical forces suchas coastal winds constantly provide power through wind turbines,with very few emissions which damage the environment.

Transformer in a transformer the voltagecan be stepped down or stepped up. Thevoltage can be manipulated by the numberof windings on the input and output, and isoften depicted as a ratio. If the primaryvoltage and secondary voltage were said tobe on a ratio of 1:10 then an input voltage of10 volts would be stepped up to 100 volts.The application of a transformer is often usedin power adapters, and often steps down 240volts to 12 volts, to enable smaller householdappliances to function correctly.

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Task 3

3.1 Operation of an electric motor:The electric motor converts electrical energy into mechanical energy.It does this by creating an electro magnetic field, which passes

current through many conductors and forms an electrical circuit.

The image above represents the workings of an electric motor. Thereis an electromagnet, which can be manipulated on and off. Thearmature core rotates to oppose the electromagnets polarity. Just asthe armature core reaches the appropriate place, the current isreversed to maintain the rotation of the core. The reversal of the

current is controlled by the commutator.

3.2a) Flemings Left Hand Rule (Motor Rule)

b)

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c)

By usingFlemings left hand rule, I was able to successfully determine thedirections of the direction of flux, the EMF and the direction of themotion of the centre axle.

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3.3

The AC generator acts in a similar way to that of the electrical motor.The difference is the end result for the output. Where the axle isturned by the increase in current, in the electrical motor, convertingelectrical energy into mechanical energy, the opposite occurs in agenerator. The mechanical energy can be converted into electricalenergy, in the form of an alternating voltage.The coil is mounted on an axel which is positioned in between amagnet.

The mechanical rotation of the coil results in a current flowingthrough the two slip rings, which are in contact with the brushes.This then transfers the current into the device being powered.

3.4a) Flemings right hand rule (the generator rule).

b)

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c)

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BibliographyThrough guidance from my lecturer, the following websites and textbooks I was able to complete this assignment:

Books

BTEC National Engineering (Mike Tooley & Lloyd Dingle)ISBN: 978-0-7506-8521-4

Catalogues

HandoutsThe Theory and Principles of Magnetism, Electromagnetism andElectromagnetic Induction

Websiteswww.en.wikipedia.org/wiki/Faraday's_law_of_inductionwww.en.wikipedia.org/wiki/Magnetwww.physics.gla.ac.uk/~kskeldon/PubSci/exhibits/E2/pelect2.gifwww.crystal-netbook.info/e148915/e149917/e149940/www.answers.com/topic/transformer?cat=technology

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Documents

BTEC NC - Electronic and Electrical Principles - Principles of Magnetism