Electromagnetism: Mutual & Self-Induction

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Mutual Induction

This occurs when two coils are in close proximity to one another

A changing magnetic field in one coil induces an emf in the other coil

Transformer

A device used to change the voltage of A.C. power supplies

It consists of a secondary coil wrapped around a primary coil, which is wrapped around a transformer core

Vi/Vo = Np/ Ns

Vi = input voltage

Vo = output voltage

Np = number of turns in the primary coil

Ns = number of turns in the secondary coil

Uses of transformers

Mobile phone chargers

Televisions

Computers

Power stations

Self-Induction

When a changing magnetic field in a coil induces an emf in the coil itself

This emf opposes the voltage across the coil (according to Lenz's law) and hence is called a back emf

Uses of Inductors

Dimmer switches

Radios

Inductor

A device used to induce a back emf

Used to reduce the current flowing in a A.C. circuit

Consists of a coil of wire with a number of turns, this is wrapped around a soft iron core

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