Magnetism

Prerequisite: physics

Magnets exert fields in a way that resembles electric fields:

One piece of magnet has little magnetic domains within itself, domains with more or less the same electron spin. A ferromagnetic metal such as iron, cobalt, and nickel have magnetic domains that do not cancel each other out, causing an uneven distribution of charge, and so it is a magnet. Hard magnets have more consistent magnetic domains, so they can be used to stroke other metals to make more magnets.

The qvB equation applies to a charge moving in a magnetic field. The BIL equation applies to a conductor carrying current, placed perpendicular to a magnetic field. We will only consider uniform magnetic fields.

In a qvB situation, the magnetic force can become a centripetal force when the magnetic field area is at least the size of the circle. In this example, the magnetic field goes into the page (and imagine that it is uniform all over the page).

This is the conventional notation for magnetic fields perpendicular to the page (me as in me reading this blog, and you as in you awkward blog).

A lot of perpendicularity is involved in magnetism. The first right hand rule applies to the BIL equation and the third to the qvB equation.

A magnetic field produced by a current involves the vacuum permeability constant µ0. The force exerted by one current carrying conductor on another depends on length, current and the other conductor's magnetic field. To know the direction of the force, use the second right hand rule to figure the direction of B between the conductors, then use the BIL right hand rule to figure the force.

One ampere is defined as the current in each wire that is one meter apart to produce 2E-7N for every meter of wire. Should not have used the equal sign there.

A solenoid is a coil of wire that makes a strong magnetic field inside when a current is applied. This makes an electromagnet, and an even stronger one with an iron rod inside.

The magnetic field of a solenoid can be calculated with this, where N is the number of loops.

Magnetic flux is the amount of theoretical magnetic field lines. The unit is weber (Wb), or (kgm^2)/(As^2). I am not sure what one Wb is supposed to mean, but it looks like kinetic energy over current to me.

If you are still wondering, magnetic field is in a sense the density of those lines. The unit is weber per meter square (Wb/m^2), or kg/(As^2), best left as Wb/m^2 for conceptualization.

Michael Faraday discovered that one can induce a current by changing the magnetic field on a conductor. This EMF can be described as ∆ϕ/∆t, yielding J/C, or volts. According to the magnetic flux equation there are several ways to induce EMF with magnetism:

1) change magnitude of magnetic field
2) change effective area of magnetic field
3) change angle of effective area
4) change effective magnetic flux on conductor (move)

Lenz's law is almost Newton's law for magnetic flux. It can be used to determine which way an induced current will run.

Below is just a nice thing to know: since changing magnetic flux induces a current, it induces an electric field to produce the current.

Huff, there. Strange stuff. Still getting my head around.