電氣專業(yè)知識題庫

電氣專業(yè)知識題庫

1.Ohm’sLaw

Ohm’sLawisafundamentalprincipleinelectricalengineeringthatdefinestherelationshipbetweenvoltage,current,andresistanceinanelectricalcircuit.Itstatesthatthecurrentpassingthroughaconductorisdirectlyproportionaltothevoltageappliedacrossit,andinverselyproportionaltotheresistanceoftheconductor.

ThemathematicalexpressionforOhm’sLawis:

V=I*R

whereVisthevoltageinvolts,Iisthecurrentinamperes,andRistheresistanceinohms.

Question1.1:

Whatisthecurrentpassingthroughaconductorwitharesistanceof10ohms,whenavoltageof50voltsisappliedacrossit?

Answer1.1:

UsingOhm’sLaw,wecancalculatethecurrentasfollows:

V=I*R

50V=I*10Ω

I=50V/10Ω

I=5A

Therefore,thecurrentpassingthroughtheconductoris5amperes.

Question1.2:

Ifthecurrentpassingthroughaconductoris2amperesandtheresistanceis20ohms,whatisthevoltageacrosstheconductor?

Answer1.2:

UsingOhm’sLaw,wecancalculatethevoltageasfollows:

V=I*R

V=2A*20Ω

V=40V

Therefore,thevoltageacrosstheconductoris40volts.

2.Kirchhoff’sLaws

Kirchhoff’sLawsaretwofundamentalprinciplesinelectricalcircuitanalysisthatareusedtodeterminethevoltageandcurrentincomplexcircuits.Theselawsarebasedontheconservationofenergyandchargeinanelectricalcircuit.

Kirchhoff’sCurrentLaw(KCL)

Kirchhoff’sCurrentLawstatesthatthesumofcurrentsenteringajunctioninacircuitisequaltothesumofcurrentsleavingthejunction.Thisisbasedontheprincipleofconservationofcharge.

Question2.1:

Inthecircuitshownbelow,calculatethecurrentI2:

Circuit

Circuit

Answer2.1:

ApplyingKirchhoff’sCurrentLawatthejunctionlabeledA,wecanwritethefollowingequation:

I1+I2=I3

WeknowthatI1=3AandI3=5A.Therefore,wecanrearrangetheequationtosolveforI2:

I2=I3-I1

I2=5A-3A

I2=2A

Therefore,thecurrentI2is2amperes.

Kirchhoff’sVoltageLaw(KVL)

Kirchhoff’sVoltageLawstatesthatthesumofthevoltagedropsacrossallelementsinaclosedloopinacircuitisequaltothesumoftheappliedvoltages.Thisisbasedontheprincipleofconservationofenergy.

Question2.2:

Inthecircuitshownbelow,calculatethevoltageV2:

Circuit

Circuit

Answer2.2:

ApplyingKirchhoff’sVoltageLawtotheclosedloopontherightsideofthecircuit,wecanwritethefollowingequation:

V1+V2=V3

WeknowthatV1=20VandV3=10V.Therefore,wecanrearrangetheequationtosolveforV2:

V2=V3-V1

V2=10V-20V

V2=-10V

Therefore,thevoltageV2is-10volts.

Conclusion

Inthisdocument,wehavecoveredtwofundamentaltopicsinelectricalengineering:Ohm’sLawandKirchhoff’sLaws.Theseconceptsareessentialforunderstandingandanalyzingelectricalcircuits.ByapplyingOhm’sLaw,wecanrelatethevoltage,current,andresistanceinacircuit.Kirchhoff’sLawshelpusanalyzecomplexcircuitsbyconsider