Magnetic Induction

First, finish up magnetic fields created by currents

A solenoid is a cylindrical coil of wire. It creates a relatively uniform magnetic field in its interior, of strength
```
              B =  mu * n * I
```
where mu is the magnetic permeability of free space, n is the number of turns of wire per meter, and I is the current through the wire.
Okay, now on to magnetic induction
Under some circumstances, a magnetic field can create an electric voltage, or an electric current. This phenomenon is called magnetic induction. It always involves change or motion of some sort.
A conductor which moves perpendicular to a magnetic field will set up an electric potential difference between its ends, of size
```
               V  =  v * L * B * sin(theta)
```
where v is the velocity of the conductor, L is its length, B is the strength of the magnetic field, and theta is the angle between the velocity of the conductor and the direction of the magnetic field.
If an induced voltage is applied to an electric circuit, it can cause an induced current to flow through the circuit.
Any work done by an induced current is taken from the kinetic energy of the moving conductor; one must apply a constant force to the conductor to keep it moving at a constant speed.