ELECTROMAGNETS
Electric currents create magnetic fields, and thus
we can create electromagnets. Here we use the
right hand rule
ELECTROMOTORS
In electromotors, the direction of the current changes, as the coil spins. The coil is placed in an outer field from a permanent magnet and hence keeps spinning, as the coil is repelled/attracted by the permanent magnet.
INDUCTION
So currents make magnetic fields, but we can ALSO use magnetic fields to induce currents (or rather time varying electric potentials):
„Induce (vb.): bring about or give rise to“ (Oxford dic.) To make this work, the magnetic field has to change.
Why?
LENZ LAW
The induced current flows such that the resulting magnetic field opposes the changes in the outer field.
GENERATORS
Generators look like electromotors that work the other
way around: movement lead to changes in magnetic fields and hence create currents.
TRANSFORMERS
The AC voltage from the power station is too high for, say, your computer. That is why your computer comes with a transformer: a primary coil and a secundary coil with a (non-conducting) iron core.
The AC current through the primary coil leads to a varying magnetic field that induces a current in the secundary coil.
TRANSFORMERS
For transformers:
Where N is the number of turns, I is the current, and U denotes the voltage.
While the power, P, (Leistung) is conserved:
