Learner Workbook Version 1

Training and Education Support Industry Skills Unit

Meadowbank

Product Code: 5631

Applied

Electromagnetism

SAMPLE

Applied Electromagnetism

© TAFE NSW (Training & Education Support Industry Skills Unit, Meadowbank)2012

First published in July 2012

This work is copyright. Any inquiries about the use of this material should be directed to the publisher.

© New South Wales Technical and Further Education Commission 2012

ISBN 978-1-74236-345-5

APPLIED ELECTROMAGNETISM

FEEDBACKWe value your opinion and welcome suggestions on how we could improve this resource manual. Keep in mind that the manual is intended to help students learn and is not a text book.

Send your comments and suggestions to:Program Manager

Trainign and Education Support Industry Skills Unit, MeadowbankMeadowbank TAFELevel 3, Building J,See Street,Meadowbank NSW 2114

Tel: (02) 9942 3200 Fax: (02) 9942 3257

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Applied Electromagnetism

© TAFE NSW (Training & Education Support Industry Skills Unit, Meadowbank)2012

Contents

Introduction .................................................................................................5

1. Magnetism ...........................................................................................7

2. Electromagnetism ...............................................................................19

3. Magnetic Circuits ................................................................................31

4. Magnetic Materials and Characteristics ..............................................43

5. Electromagnetic Induction .................................................................55

6. Inductors ...........................................................................................67

7. Inductance and Mutual Inductance ....................................................77

8. Principles of Machines and Devices ....................................................89

9. d.c. Machine Construction, Testing and Maintenance ..........................99

10. d.c. Generators - Characteristics & Applications ...............................109

11. d.c. Motor - Operating Principles and Types .....................................121

12. d.c. Motor - Characteristics and Applications ....................................133

13. MachineLossesandEfficiency ..........................................................145

14. d.c. Motor Starting, Braking and Speed Control ................................151

15. Specialised d.c. Machines .................................................................159

Review Questions - Answers ....................................................................165

Sample Assessment ..................................................................................181

Sample theory test 1 .......................................................................181

Sample theory test 2 .......................................................................187

Sample theory test 3 .......................................................................194

Practical Test ...................................................................................204

Theory Test 1 - Answers ...........................................................................207

Theory Test 2 - Answers ...........................................................................209

Theory Test 3 - Answers ...........................................................................211

Summary of technical information ............................................................215

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Applied Electromagnetism

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Risk Assessment Terminology

Supervision Level:

D Direct This means the personal supervision of a learner, at all times, on a direct and constant basis, within visual contact and/or earshot. Constant basis refers to the continuous supervision of tasks’ beingperformedforthefirsttimeanduntilskillisdemonstratedfor the complexity of the task and work environment.

G General This means the learner does not require constant attendance of the supervisor but requires personal contact with an experienced worker on a recurrent basis when working. Periodic supervision means being under instruction and direction for tasks being formed with checks and test being made prior to the commissioning of apparatus/equipment.

B Broad This means the learner does not require constant supervision but requires personal contact with an experienced worker on at least a regular/occasional basis when working. Occasional supervision means being under instruction and directino with checks being carried out on completion of multi-tasks.

Risk Classes:

A high risk Potential death or permanent disablement.

B medium risk Potential serious injury/illness and temporary disablement.

C low risk Potential minor injury, no lost time.

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Applied Electromagnetism

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1. Magnetism

PurposeIn this topic you will learn about the principles of magnetism.

ObjectivesAt the end of this topic you should be able to:

• sketchthemagneticfieldpatternofbarandhorse-shoemagnets

• describe how magnets can attract and repel when brought in contact with each other

• describe the principle of magnetic screening

• list practical applications of magnets.

Technical informationYouwillfindtheinformationtoundertakethistopicinthefollowingreferences.Atleastone reference text should be used.

References for this topic• Jenneson J.R., 2010, Electrical Principles for the Electrical Trades, 6th Ed., McGraw-

Hill, Sydney• Hampson, J., 2011, Electrical Trade Principles - A Practical Approach, 2nd Ed.,

Pearson Education, Sydney.

• Phillips P., 2012, Electrical Principles, 2nd Ed., Cengage Learning, Melbourne.

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Applied Electromagnetism

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Practicalexercise: Magneticfieldsofpermanentmagnetsandscreening

TaskToobserveandmapthemagneticfieldpatternswhenbarmagnetsarepositionedneareachotherindifferentconfigurations.

To note the effect of placing different types of metal within the area of the magnetic fieldscreatedbybarmagnets.

ObjectivesAt the completion of this practical exercise you should be able to:demonstratethepatternofthemagneticfieldthatsurroundspermanentmagnetsdemonstratetheeffectonamagneticfieldproducedbyasinglemagnetbyapieceofdemagnetisedmagneticmaterialplacedinthefield

demonstratehowregionscanbeisolatedfromtheinfluenceofadjacentmagnetsbysurrounding the region with a low reluctance path

demonstratetheeffectofthefluxdistributionofmagneticfieldsbytheinsertionofmagnetic and non-magnetic substances; and

demonstratethescreening,orshielding,ofareasinmagneticfieldsbyappropriatelyplaced low reluctance materials.

EquipmentYourteacherwillprovideyouwiththespecificationsoftheequipmenttobeused.Bar magnets – 3 off.Horse shoe magnet – 1 offPiece of mild steel of approximately the same dimensions as the magnets.Piece of brass of similar dimensions to the magnets.Mild steel ring Brass ring Several sheets of cardboard or heavy paper.Aquantityofironfilings.Note:suggestedspecificationforbrassandsteelrings: - same height as the magnets - outside diameter approximately 30 mm - inside diameter of approximately 5 mm.

Risk AssessmentIdentify any hazards, list the supervision level (D, G or B), list the risk class (A, B or C) and list control measures required in the table below:

HazardIdentification Supervision Level Risk Class Control Measures

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Applied Electromagnetism

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N S

Figure 1.3

N S

Figure 1.4

N N

Figure 1.5

N S

S N

N S

Figure 1.2Figure 1.1

Figure 1.6

N S

N S

Procedure1. Cover each arrangement of the magnets shown in Figures 1.1 to 1.12 with a

pieceofcardboard(orclearperspexsheet).Sprinkletheironfilingsevenlyandlightlyoverthecardboardandgentlytapthecardboarduntilthefilingsformapattern.

2. For each arrangement, neatly draw the respective patterns that represent the magneticfieldasillustratedbytheironfilings.

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Applied Electromagnetism

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Figure 1.7

N S

N

Figure 1.8

N

S

N

N N

NS S

S

Figure 1.9

brass

N

barBrassbar

S

Figure 1.10

Steel

Figure 1.12

N

S

Brassring

Figure 1.11

N

S

Mild steelring

N

Have your teacher check your results

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Applied Electromagnetism

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Observations1. Explainwhytheironfilingsformeddifferentpatternsforeachofthecombinations

of Figure 1.1 to 1.12.

2. DrawthefieldpatternofFigure1.10whenthebrassbarwasreplacedwithanother steel bar.

3. ExplainwhythefieldpatternsofFigure1.11and1.12aredifferentwhentherings are the same dimensions and the magnets are in the same locations.

4. Indicate the direction of the magnetic lines of force on each Figure 1.1 to 1.12 (use the standard convention).

5. State in your own words what is meant by the term “screening” or “shielding”.

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Applied Electromagnetism

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6. List some practical applications of magnetic shielding.

7. What is meant by the statement “iron is more permeable than air?”

Have your teacher check your observations

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