Electromagnetic Induction - Solved Exercise - Basic Concepts of Physics | Exercises Physics

1)Cananelectronplacedatrestinamagneticfieldbesetinmotionbythemagneticfield?Whatifwereplacedatrest

inanelectricfield?

Anelectronatrestinamagneticfieldexperiencesnoforce,socannotbesetinmotionbythemagneticfield.Ifitwere

placedatrestinanelectricfield,itwillaccelerateundertheelectrostaticforce.Theelectrostaticforcedependsonlyon

thechargeandthefieldstrength,whilethemagneticforcedependsonthecharge’svelocityaswell,andiszeroifthe

velocityiszero,orifthechargemovesparalleltothefield.



2)Ifyouhadtwobarsofiron,onemagnetizedandtheothernot,andnoothermaterialsathand,canyouthinkofaway

ofdeterminingwhichbarwasthemagnet?

PlacetheminaT‐shapedconfiguration.Then,ifthereisanetattraction,thentheironbarthatformsthe

verticalpartoftheTisthemagnet.Iftheydonotattract,theironbarthatformsthehorizontal(top)oftheT

isthemagnet.

N S

    



   



Someofyouhadotherveryinterestingideasonthis,e.g.usingtheprinciplesofelectromagneticinduction…



3)Amagicianplacesanaluminumringonatable,underwhichishiddenanelectromagnet(i.e.acoilofwirethatmay

carryacurrent).Whenthemagiciansays“abracadabra”(anddiscreetlypushesaswitchthatturnsonthecurrentinthe

coil),theringjumpsintheair.Explainhismagictrack.

Thechangingmagneticfieldproducedwhenthecurrentstartstoflowinthecoilinducesacurrentinthealuminumring,

sincetheringliesinthemagneticfieldofthecoil.Thiscurrent,inturn,generatesamagneticfieldthatopposesthefield

producedbythemagnetunderthetable.Thealuminumringbecomes,momentarily,amagnetthatisrepelledbythe

hiddenmagnet,henceitjumpsintheair.



4)Cananefficienttransformerstepupenergy?Explainyouranswer.

No.Astep‐uptransformerincreasethevoltage,butthecurrentdecreasesproportionallysothatthetotalpoweristhe

same.Nodevicecanstepupenergy–thisisafundamentallawinphysics,energycannotbecreatednordestroyed.

NNnNNNNi

Nonetattractionhere

sincenonet

magnetizationofthis

ironbar–equal

distancebtnNandS

ofthemagnet

Netattractionhere

sincetopironbargets

magnetized–closerto

onepoleofmagnet

thantheother.



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in Canan electric an electron field? placed at rest in a magnetic field be set in motion by the magnetic field? What if were placed at rest An placed electron at rest at inrest an in electric a magnetic field, fieldit will experiences accelerate under no force, the soelectrostatic cannot be setforce. in motionThe electrostatic by the magnetic force depends field. If itonly were on the velocity charge is zero, and the or if field the strength,charge moves while parallel the magnetic to the field.force depends on the charge’s velocity as well, and is zero if the
If you had of two determining bars of iron, which one bar magnetized was the magnet? and the other not, and no other materials at hand, can you think of a way Place vertical them part in of a the T‐shaped T is the configuration. magnet. If they Then, do notif there attract, is a thenet ironattraction, bar that then forms the the iron horizontal bar that forms(top) ofthe the T is the N magnet. S

Some of you had other very interesting ideas on this, e.g. using the principles of electromagnetic induction…

carry A magician a current). places When an the aluminum magician ring says on “abracadabra” a table, under (andwhich discreetly is hidden pushes an electromagnet a switch that (i.e. turns a coil on ofthe wire current that inmay the coil), The changing the ring jumpsmagnetic in the field air. produced Explain hiswhen magic the track. current starts to flow in the coil induces a current in the aluminum ring, since produced the ring by the lies magnet in the magnetic under the field table. of theThe coil. aluminum This current, ring becomes, in turn, generatesmomentarily, a magnetic a magnet field that that is repelledopposes bythe the field hidden magnet, hence it jumps in the air.

No.^ 4)^ Can A step^ an^ ‐efficientup transformer^ transformer increase^ step the^ up voltage,energy? butExplain the yourcurrent^ answer. decreases proportionally so that the total power is the same. No device can step up energy – this is a fundamental law in physics, energy cannot be created nor destroyed.

NNNNnNNNNi No since net no attraction net here magnetization iron bar – equal of this distance of the magnet btn N and S

Net since attraction top iron barhere gets magnetized one pole of magnet– closer to than the other.

Electromagnetic Induction - Solved Exercise - Basic Concepts of Physics, Exercises of Physics

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