Module – I, Lecture-5
Dynamically induced emf
Theemfinducedinacoilduetorelativemotionoftheconductorandthemagneticfieldis called dynamicallyinduced emf.
Example:dcgeneratorworksontheprincipleofdynamicallyinducedemfintheconductors which arehoused in a revolvingarmaturelyingwithin magnetic field
Statically induced e.m.f
Thechangeinfluxlineswithrespecttocoilcanbeachievedwithoutphysicallymoving thecoilorthemagnet.Suchinducede.m.f.inacoilwhichiswithoutphysicalmovementofcoil or amagnet is called staticallyinducede.m.f.
Tohaveaninducede.m.ftheremustbechangeinfluxassociatedwithacoil.Sucha changeinfluxcan beachievedwithoutany physicalmovementby increasinganddecreasingthe current producingthe fluxrapidly,with time.
Consideranelectromagnetwhichisproducingthenecessaryfluxforproducinge.m.f. Nowletcurrentthroughthecoilofanelectromagnetbeanalternatingone.Suchalternating currentmeansitchangesitsmagnitudeperiodicallywithtime.Thisproducesthefluxwhichis
alsoalternatingi.e.changingwithtime.Thusthereexistsassociatedwithcoilplacedinthe
viscinityof anelectromagnet. This is responsiblefor producing ane.m.fin the coil. Thisis called staticallyinduced e.m.f.
Thereisnophysicalmovementofmagnetorconductor;itisthealternatingsupplywhich is responsible for such aninduced e.m.f.
Such typeof an inducede.m.f. is available in transformers.
Dynamicallyinducede.m.f.
Thechangeinthefluxlinkingwithacoil,conductororcircuitcanbebroughtaboutby itsmotionrelativetomagneticfield.Thisispossiblebymovingfluxwithrespecttocoil conductororcircuitoritispossiblebymovingconductor,coil,circuitwithrespecttostationary magnetic flux.
Suchaninducede.m.f.whichisduetophysicalmovementofcoil,conductorwith respecttofluxormovementofmagnetwithrespectwithtostationarycoil,conductoriscalled dynamicallyinducede.m.f.ormotionalinducede.m.f.
Thistypeofinducede.m.f.isavailableintherotatingmachinessuchasalternators, generator etc.
Selfinductance:
AccordingtoLenz‟slawthedirectionofthisinducede.m.f.willbesoastoopposethe causeproducingit.ThecauseisthecurrentIhenceself-inducede.m.fwilltry tosetupacurrent whichisinoppositedirectiontothatofcurrentI.Whencurrentisincreased,self-inducede.m.f. reducesthecurrenttriestokeeptoitsoriginalvalue.Ifcurrentisdecreased,self-inducede.m.f. increasesthecurrentandtriestomaintainitbacktoitsoriginalvalue.Soanychangeincurrent through coilis opposed bythecoil.
Thispropertyofthecoilwhichopposesanychangeinthecurrentpassingthroughitis called self-inductance oronlyinductance.
It is analogous to electrical inertia or electromagnetic inertia.
Theformula for self-inductanceisgiven by,
L=
It can bedefinedas fluxlinkages per ampere current in it.Its unit is Henry(H)