IntroductiontoElectricalTheory

Description

Workingasanelectrician requires manyskills.Thephysical demands ofthejob are oneimportantpartof the skills needed to succeed. Reading andcommunication skills are otheraspects one must develop and improve to beasuccessfulworker in the electrical field. Electricaltheory is a basic building block thatevery potential electrician must understand from the start.

Electricity makesnosound,doesn’thaveanodour,andcan’t be seen, so understandingthepoweryou’redealingwithintheory,helpstomakeyouandotherssafe. Electrical theoryisimportant tounderstand thefunctionand operationof electrical equipment to ensure properinstallationandto completetasks such as troubleshooting electrical systems and equipment.Much hasto be learnedtofullyunderstand electrical theory,andittakesyearstomaster.Thisactivity planwillcover thebasics, and it should be understoodthat students will needtocontinuetodeveloptheirmathand science proficiencies if theyintendto become anelectrician.

LessonOutcomes

The student willbeableto:

•Understand a basic electric circuit

•KnowhowtouseOhm’slawinbasiccircuitcalculations

•Understand the difference between directcurrent and alternating current

•Understandhowamultimeter issafely used to testreadings ofanAC circuit

•Understand basic series andparallel circuit

Assumptions

•Studentswillhave little or noknowledgeofOhm’slawand electric circuits.

Terminology

Alternatingcurrent(AC):anelectriccurrentthatreversesdirectionandmagnitudeinacircuitatregularintervals.

Closedcircuit:aclosedpathorcircuitcapableofbeingfollowedbyanelectriccurrent.

Conductor:amaterialorobjectthatallowscurrenttoflowthroughit.Copperandaluminum arecommonconductorsinelectricalsystems.

Current:theamountofelectronsflowingpastaspecifiedcircuitpointperunittime,expressedinamperes,oramps.

Directcurrent:anelectriccurrentflowinginonedirectiononly.

Insulator:asubstanceordevicethatdoesnotreadilyconductelectricity.

Thisworkis licensedunder aCreativeCommonsAttribution-NonCommercial-ShareAlike4.0InternationalLicenseunlessotherwiseindicated.

Multimeter:anelectricaltestinstrumentthatcanmeasure severalvalues, usuallyvoltage,current,andresistance.

Ohm’slaw:alawinelectricitythatstatesthatthecurrent (ampsexpressedasI)inacircuitisproportionaltothe potential difference (voltage, expressedas E) divided by theresistanceofthe

circuit(ohms,expressedasR),I=E

R

orE=I×RorR=E

I

Opencircuit:anopenpath preventingtheflowofcurrent.

Parallelcircuit:electricalcomponentsorcircuitsconnectedtocommonpointsateachend,ratherthanonetoanotherinsequence.Morethanonepathforcurrentto flow.

Resistance:theoppositionofabodyorsubstancetocurrentpassingthroughit,resultinginachangeofelectricalenergy intoanotherformofenergycommonlyheatorlight.

Seriescircuit:electricalcircuitsorcomponentsarrangedsothatthecurrentpassesthrougheach successively. Onepathforcurrent flow.

Shortcircuit:apathoflowresistanceallowingahighcurrentto flow.

Voltage:electromotiveforceor potentialdifference,expressedinvoltageorvolts. Electricalpressure.

Watt:theSIunitofpower, equivalent to1joulepersecond,correspondingtothepowerinanelectriccircuitinwhichthe potential differenceis1 volt andthecurrent1ampere.

Power formula,P(watts)=E×IorP=I2×R

EstimatedTime

2–3 hours

RecommendedNumberofStudents

20, based onBCTechnology Educators’Best PracticeGuide

Smallgroupsof2–4 based on equipmentavailable

Facilities

Technologyeducation shopwith benches

Tools

•ACcircuit

•teacherdemonstration:

–multimeter

–scientific calculator

Materials

•Battery holders(2)

•1.5-voltbatteries(2)

•3-voltlightboards or connecting wires

•Light bulbs

•Alligatorclips

Optional

Scientific calculators

Resources

BasicTheoryOhm’sLaw

AnAnalogyforOhm’sLaw

SampleCurriculum:CurrentElectricity

HowtoDrawSimpleElectricCircuitsLesson

©WorkSafeBC. Used with permission from the publication ”WorkingSafely Around Electricity.”

Activity:CurrentElectricityExperiment

Howthis activity issequencedisto bedetermined by the teacher. There are someresourcestohelpexplainOhm’slaw,andtheteachermightwanttostartwith a small“theoryofOhm’s law”lesson, or completethe lesson after theactivity.Thedepthofthis activity isbased on students’priorlevel of knowledge.Studentswilldo a review of a few simple DC circuitsthat likelywill havebeencoveredin Science 9.Theseexperimentsshouldhelpstudentsunderstandhowresistivesources reactwhen placed inseries and parallel circuits.

OptionalActivity

If DC circuitmaterialsarenotreadilyavailable,theteachermayshowtheBasicTheoryOhm’sLawvideo(seetheResourcessection)torefreshstudents’knowledgeof a basic electric circuitandOhm’slaw.Thevideo could alsosupplementthe DC circuitactivity.The“AnalogyforOhm’slaw” link(seetheResourcessection) could also be usefultohelpexplainOhm’slawtostudentshaving difficulty understandingthe concept. TheworksheetprovidedwillallowstudentstopractisecalculatingbasicOhm’slawproblems.

EvaluationGuidelines

Thestudent:

•Workssafely

•Followsinstructions

•Demonstrates knowledge andunderstanding

•Answersquestions correctly

Ohm’sLawProblems

Showyourwork.

1.3 voltsisapplied across a 6-ohmresistor.Whatisthecurrentflowing?

2.A 1.2-ohmresistorpasses a currentof 0.2 amps.Whatisthevoltage across it?

3.Whatisthevoltageof a circuitwith a resistanceof 250 ohmsand a currentof0.95amps?

4.A small electricalpump is labelled witha rating of 3 amps and aresistance of 40ohms.Atwhat voltage is it designed tooperate?

5.A9-volt battery ishooked up to a lightbulbwith arating of 3ohms.Howmuch currentpasses throughthe light?

6.A lampispluggedintothewalloutlet, which isproviding110volts.Anammeter attached

tothelampshows 2 ampsflowingthroughthecircuit.Howmanyohmsofresistanceisthelamp providing?

7.Ifyourskinhas a resistanceof10,000ohmsandyoutouch a 9-volt battery,whatcurrentwillflowthroughyou?

8.Whatcurrentwillflowthroughyourbodywith a skinresistanceof10,000ohms, if youtouch120-volthousepotential?

9.Whenyouaresoakedinseawater,yourresistanceisloweredto 1000 ohms.Nowhowmuchcurrentwillflowthroughyou if youtouchthe 9-volt battery?

10.Whenyouaresoakedinseawater,whatcurrentwillflowthroughyou if youtouchthe120-volt house potential?

11.Howmuchcurrentflowingthroughyourbodyisconsideredfatal?

Answers

E=9I= ?R=3

E=IRE=110

I=2

I= IR

I=9

3

I=3A

R= ?R=E

I

R=110

2

R=55

7. Ifyour skin has a resistanceof10,000ohmsandyoutouch a 9-voltbattery,whatcurrentwillflowthroughyou?
E=IRE= 9I= ?
R=10,000
I=E / 8.Whatcurrentwillflowthroughyourbodywith a skinresistanceof10,000ohms, ifyoutouch120-volthousepotential?
E=IRE=120I=?
R=10,000
I=E
R
I=9
10,000
I=0.0009A
9. Whenyouare soakedinseawater,yourresistanceisloweredto 1000 ohms.Nowhowmuchcurrentwillflowthroughyou ifyou touchthe9-voltbattery? / R
I= 120
10,000
I=0.12A
10.Whenyouaresoakedinseawater,whatcurrentwillflowthroughyou if youtouchthe120-volthousepotential?

E=IRE= 9I=?

R=1000

I=E

R

I= 9

1000

I=0.009A

E=IRE=120I=?

R=1000

I=E

R

I=120

1000

I=0.12A

11.Howmuchcurrentflowingthroughyourbodyisconsideredfatal?

0.05A,or50mA