Electromagnetic Induction

Electromagnetic Induction

What’s Next?

Electromagnetic Induction Faraday’s Discovery Electromotive Force Magnetic Flux Electric Generators Lenz’s Law Self-Inductance Transformers

What do we know? Hans Christian Oersted showed that moving

charges create a magnetic field.

Faraday’s Hypothesis

If moving charges produced a magnetic field, could a moving or changing magnetic field produce a current?

Faraday’s Discovery

Faraday discovered that he could induce current by moving a wire loop through a magnetic field or moving the magnetic field through a wire loop.

Faraday’s Discovery is known as Electromagnetic Induction

Faraday's Discovery

Electromotive Force Last week we learned the Lorentz Force.

FB = qvB sinθ = BIL sinθ

When a conductor moves through a magnetic field, a force is exerted on these charges causing them to separate, inducing an EMF.

x x x x x x x x x

x x x x x x x x x

x x x x x x x x x

vF

+

-

L

Electromotive Force We know: W = Fd and V = W/q.

V = Fd/q

Using algebra and solving for F:

F = Vq/d F = qvB

Set these two relationships equal to one another and then solve for V, which will now be represented as EMF:

EMF (V) = vBL

Where: L is the length of a conductor passing through a magnetic field.EMF = Electromotive Force (Volts)

Electromagnetic Induction

Why is it important? Motors Generators Transformers

Electric Generators Invented by Michael Faraday. Convert mechanical energy into electrical

energy. Similar to an electric motor, but function in an

opposite manner. Electrical power generation is the foundation by

which electricity is supplied to homes and businesses around the world.

Electricity is generated in many ways - hydroelectric, nuclear, coal, gas, oil fired, wind solar, geothermal.

Magnetic Flux

What is magnetic flux? Like electric flux A measure of the strength of the magnetic field, B,

passing through a surface perpendicular to the field. For a bar magnet, the flux is maximum at the poles. The more magnetic field lines, the higher the flux.

=BAcos

Lenz’s Law The induced EMF resulting from a changing

magnetic flux has a polarity that leads to an induced current whose direction is such that the induced magnetic field opposes the original flux change.

If the magnetic field is increasing, a current will develop to oppose the increasing magnetic field.

If the magnetic field is decreasing, a current will develop to create a magnetic field in the same direction as the one that is decreasing.

A current will form that attempts to keep the magnetic field constant.

Lenz’s Law abides by the laws of conservation of energy.

Lenz’s Law

Lenz's Law

Key Ideas Electromagnetic induction: is the process

by which current is generated by moving a conductor through a magnetic field or a magnetic field through a conductor.

The induced current is maximum when the relative motion of the conductor is perpendicular to the magnetic field.

The induced voltage is called EMF (=vBL). Magnetic flux is a measure of the strength

of the magnetic field passing through a surface.

Key Ideas A generator is a device that converts

mechanical energy into electrical energy.

Generators are similar to motors. Lenz’s Law: The induced EMF

resulting from a changing magnetic flux has a polarity that leads to an induced current whose direction is such that the induced magnetic field opposes the original flux change.