InterviewSolution
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InterviewSolution
| 1. |
Describlethe constructionand workingof an AC generator ( an alternator). |
Answer» Solution :An electric genertor is a devicethat converts mechanical energyinto electrical energy . Itsworking is basedon electromagneticinduction.  Construction : (1) Figure13.30 (a) shownsthe constructionof an AC generator . Itconsists of a rectangularcoilABCD placedbetweenthe twopoles of a permgent mganet . (2) Two ends of this coilare connected to the two metal (copper) rings`R_(1)`and `R_(2)`. Theinner side of theseringsare insulated . (3) The twoconductingstationary brushed `B_(1)` and `B_(2)` are kept pressedseparatelyon the rings `R_(1)`and `R_(2)`respectively . (4) The tworings `R_(1)` and `R_(2)`areinternallyattachedto an axle .Theaxlemay be mechanicallyrotated to from outsidetorotate the COIL inside the mgneticfield . (5) Outerendsof the twobrushes are connected to thegalvanometerto showthe flowof currentin the given external circuit . Working : (1) Suppose, theaxleattached to thetworingsis rotatedsuchthat the arm AB moves up and the arm CDmoves down in the magneticfield produced by the permanent magnet . THENTHE coil ABCD rotates clockwisein the arrangement SHOWN in the figure . By applying Fleming.s right hand rule , we findthat the induced currents areset upin thse arms along thedirectionAB and CD . Thismeans that the currentin external circuit flows from brush `B_(2)`to `B_(1)` [Ifthe COILIS madeof largenumberof turns,the currentgeneratedin eachturn adds up to givea largecurrentthrough the coil] . (2) Afterhalfa rotation , arm CD startsmovingup and AB movingdown .Asaresult ,the directionof the inducedcurrentsin both the arms change , givingrise tothe net induced current in the direction DCBA . Thismeans that the currentin theexternalcircuitnow flows from brush `B_(1)` to `B_(2)` (3) Thus, after everyhalf rotation the directionof the currentin the respective arms changes. Sucha current ,whichchanges directionafter equal INTERVAL of time, is calledan alternatingcurrent (abbreviated as AC). |
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