Electromagnetic induction

Page 1

Generating electricity

It is the process whereby a conductor and a magnetic field are moved relative to eachother to induce a current or e.m.f.

size of induced current or emf depends on:

For a straight wire:

magnitude of magnetic flux density

length of wire in field

speed of movement of wire

For a coil of a wire:

magnitude of flux density

cross sectional area of coil

number of turns of wire

rate at which the coil turns in field

Explaining electromagnetic induction

relative movement of a conductor and a magnetic field induces a current in conductor when its part of a circuit.

Cutting magnetic field lines

As wire moves in magnetic field, it cuts the across the field. Remove it and it cuts across field in opposite direction.

If we use a coil of a wire. For a coil of N turns, the effect is N times greater for a single turn of wire.

Current direction

Fleming's right hand rule

Induced e.m.f.

Magnetic flux and magnetic flux linkage

how to calculate induced e.m.f. and how to find its direction

B=F/IL

Magnetic flux (phi) =BA where B is component of magnetic flux density perpendicular to area.

magnetic flux =Bcos(theta) x A

when theta = 90 (when parallel to area) magnetic flux is zero

For a coil with N turns, magnetic flux linkage is product of magnetic flux and number of turns N:

Magnetic flux linkage= Nx (phi)magnetic flux

or magnetic flux linkage =BANcos(theta)

An e.m.f. is induced whenever there is a change in magnetic flux. Since magnetic flux =BAcos(theta), e.m.f. can be induced by:

changing magnetic flux density B

changnig area A of circuit

chaging angle (theta)

Faraday's law of electormagnetic induction

when conductor cuts across lines of magnetic flux e.g. when a coil is rotated in a magnetic field so magnetic flux linking coil changes.

We can use Faraday's law of ele..induction to determine magnitude of induced e.m.f. in circuit.

The magnitude of the induced e.m.f. is proportional to the rate of change of magnetic flux linkage.