Electromagnetism and Electromagnetic Induction

Electromagnetism

 Recall that the motion of charges leads to magnetic fields.  

 If you have charge traveling through a wire, electrons can be thought of as moving together – this causes a magnetic field, also known as electromagnetism.  The magnetic field caused by a current passing through a wire is often small, but if you coil the wire upon itself, the magnetic fields “add up”.  Several hundred turns of wire (with current running through it) can produced quite a strong electromagnet. 
A coil with current running through it can naturally react to a permanent magnet – if this is engineered well, we have a motor.  See illustrations and demos in class.



Below:  basic motors







Electromagnetic Induction
So, current causes magnetism – something shown in the early 19th century by Hans Oersted.  As it happens, the reverse is also true – magnetism can cause current, but there must be some relative CHANGE in the magnetic field or location of conductor.   There must be relative motion – either coil or magnet must move, relative to the other.  This was first shown by Michael Faraday.
This phenomenon, wherein a change in magnetic field relative to a conductor, generates electric current is called “electromagnetic induction.”  It is the secret to understanding generators.  If something, say moving water from Niagara Falls, can cause a coil of wire (in a turbine) to spin, current is generated.  More spins of wire means more current.
It’s all about moving conductors in magnetic fields.




In conclusion:
Electromagnetism:
Current (moving charges) cause a Magnetic Field

Electromagnetic Induction:
Change in magnetic field (through conductor), or vice versa (conductor moving through a magnetic field) causes an electric current.  It's about RELATIVE MOTION between conductor (metal) and magnetic field.

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