Electromagnetic inductionCopy

Learning Objectives

• Show understanding that a conductor moving across a magnetic field or a changing magnetic field linking with a conductor can induce an e.m.f. in the conductor
• Describe an experiment to demonstrate electromagnetic induction
• State the factors affecting the magnitude of an induced e.m.f.
• Show understanding that the direction of an induced e.m.f. opposes the change causing it
• State and use the relative directions of force, field and induced current

Contents to learn

Induced e.m.f.

Whenever a magnetic field is changed across the conductor, an e.m.f. induces across it.  So there will be flow of induced electric current in the conductor.

If a bar magnet is pushed in to a coil, an e.m.f. is induced in the coil and induced electric current flows through it as shown below.

If a bar magnet is pulled out of the coil, again an e.m.f. induces across the coil and induced electric current flows through it but in this case the direction of the current reverses.

Factors affecting the magnitude of induced e.m.f.

The magnitude of induced e.m.f. and of course induced electric current can be increased by the following way:

• Using a strong magnet (increasing the strength of magnetic field).
• increasing the number of turns in the coil.
• moving the magnet faster.

Note: If the bar magnet is kept inside the coil at rest, no magnetic lines of forces will be cut ( i.e. magnetic field will not be changed across the conductor), so no e.m.f. will be induced.

Lenz’s law

Induced electric current oppose the movement of the magnet, which is the cause of its production. This fact was stated by Lenz.

This law states that ” the direction of induced electric current is always so as to oppose the change which causes the induced electric current”.