# Arduino Netduino: Hall Effect, Keyes 003 Magnetic sensor and the General Theory of Electromagnetism

Hall Effect or Magnetic ring, in my blogs I have discussed both, and both of these devices detect magnetic fields.  As you may know, from Maxwell’s General Theory of Electromagnetism, we discover that many professors struggle with making electromagnetism fun!  Ok, that wasn’t the point, if you are not familiar with the General Theory of Electromagnetism, you live in a civilization that is based on the concepts laid down by the General Theory.  If you are reading this on a computer, and I doubt that any of my blogs have been printed out, so that is a safe assumption you are.

For a more in-depth take a  look at the General Theory of Electromagnetism, briefly they are, which look complicated, but in reality they are pretty easy to implement in the physical world.  The integral symbol with the circle on it is a “closed” integral and first described by Stokes (not me, a distant relative):

Equations reference is: http://galileoandeinstein.physics.virginia.edu/more_stuff/Maxwell_Eq.html

1. Gauss’ Law for electric fields:   (The integral of the outgoing electric field over an area enclosing a volume equals the total charge inside, in appropriate units.)
2. The corresponding formula for magnetic fields:   (No magnetic charge exists: no “monopoles”.)
3. Faraday’s Law of Magnetic Induction:    The first term is integrated round a closed line, usually a wire, and gives the total voltage change around the circuit, which is generated by a varying magnetic field threading through the circuit.
4. Ampere’s Law plus Maxwell’s displacement current:    This gives the total magnetic force around a circuit in terms of the current through the circuit, plus any varying electric field through the circuit (that’s the “displacement current”).

Once you understand these equations well enough  to wear them on at T-Shirt or talk about them at a dinner party, then you are taking this far too seriously.

Ok that is it for the funky equations.  If you go into physics or electrical engineering, the will haunt your dreams, for everyone else, let’s more on to the next blog where we discuss how the Hall Effect Transistor and circuit works, as well as how to use it.