# 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.

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