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1 | P a g e h t t p s : / / w w w . c i e n o t e s . c o m / Physics (A-level) Electromagnetic induction (Chapter 23): For a straight wire, the induced current or e.m.f. depends on: The magnitude of the magnetic flux density The length of the wire in the field The speed of movement of the wire For a coil of wire, the induced current or e.m.f. depends on: The magnitude of the magnetic flux density The cross-sectional area of the coil The number of turns of wire The rate at which the coil turns in the field In electromagnetic induction, Fleming’s right -hand (generator) rule is used: By pushing the wire through the magnetic field, work is done and transformed into electrical energy (e.m.f.) We can picture the magnetic flux density as the number of magnetic field lines passing through a region per unit area ; we can picture magnetic flux as the total number of magnetic field lines passing through an area A ; therefore the magnetic flux Φ is defined as the product of magnetic flux density and the cross-sectional area A (normal to the field): For an coil with N turns, the magnetic flux linkage is defined as the product of the magnetic flux and the number of turns:
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2 | P a g e h t t p s : / / w w w . c i e n o t e s . c o m / The unit for magnetix flux or flux linkage is the Weber (Wb) One Weber (1 Wb) is the flux that passes through an area of 1m 2 when the magnetic flux density is 1 T. (1Wb = 1 Tm 2 ) e.m.f. is induced whenever there is a change in magnetic flux linking the circuit; this can be done by: Changing the magnetic flux density B Changing the area A of the circuit Changing the angle Electromagnetic induction occurs whenever a conductor cuts across lines of magnetic flux Faraday’s law of electromagnetic induction (to determine the magnitude of the induced e.m.f. in a circuit): the magnitude of the induced e.m.f. is proportional to the rate of change of magnetic flux linkage Lenz’s law : any induced current or e.m.f. will be established in a direction so as to produce effects which oppose the change that is producing it Conservation of energy in electromagnetic induction:
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