(k) Electromagnetic Induction

Learning Objectives

• (a) deduce from Faraday’s experiments on electromagnetic induction or other appropriate experiments:

(i) that a changing magnetic field can induce an e.m.f. in a circuit

(ii) that the direction of the induced e.m.f. opposes the change producing it

(iii) the factors affecting the magnitude of the induced e.m.f.

• (b) deduce the direction of the induced current from Fleming’s RH rule and Lenz’s Law

When there is a change in the magnetic flux linking a conductor, an electromotive force (e.m.f.) is induced between the ends of the conductor. This is called electromagnetic induction. If the conductor forms part of a circuit, the induced e.m.f. produces an induced current.

Visit the websites to do a virtual simulation of Faraday's experiments.

Faraday's iron ring experiment :- http://micro.magnet.fsu.edu/electromag/java/faraday/

Faraday's solenoid experiement :- http://micro.magnet.fsu.edu/electromag/java/faraday2/

The magnitude of the induced e.m.f. in the conductor can be increased by:-

• increasing the strength of the magnet

• increasing the length of wire within the magnetic field (i.e. increasing the number of turns of the solenoid)

• increasing the relative speed between the magnet or conductor.

A simulation of Lenz's law ;- http://micro.magnet.fsu.edu/electromag/java/lenzlaw/

The direction of the induced e.m.f can also be determine by using the Fleming's right hand rule which states that if the thumb and first two fingers of the right hand are held at right angles to each other, where the thumb points in the direction of the motion, the first finger points in the direction of the magnetic field, then the second finger points in the direction of the induced e.m.f and hence in the direction of the induced current in a closed circuit.

Verify the direction of the induced current with the Fleming Right Hand Rule for the following examples.