What is an Electromagnetism?

As it turns out, electricity and magnetism are fundamentally linked. Every electric or magnetic phenomena you’ve ever encountered is due to the electromagnetic force, and the electric and magnetic fields that it gives rise to. In fact, electromagnetism is one of the 4 fundamental forces in physics: gravity, electromagnetism, the weak nuclear force, and the strong nuclear force. Actually, under some conditions, it appears that the weak force and electromagnetism combine into one force, however that is well outside the scope of my understanding. Electromagnetism is also the origin of the discovery of quantum physics.

Charge

The fundamental unit of electromagnetism is charge. If this reminds you of charging a battery, that’s not a coincidence. You might be aware protons and electrons are electrically charged particles. This means that they have a non-zero electrical charge. Specifically they both have opposite charges of +1.6x10^-19 coulombs © for a proton, and -1.6x10^-19C for an electron. A coulomb is a unit of electrical charge. You may be more familiar with the unit mAh or milliamp-hours, which is also a unit of charge equal to 3.6 coulombs. Also, it’s probably what the charge capacity of the battery in your phone is given in. If your phone has a 5000mAh battery, then it has a charge capacity of 18000 (5000*3.6) coulombs. Which means that the fully charged battery has the potential to flow 1.125x10²³ (18000/1.6x10^-19) electrons through the circuits it is powering before it needs to be charged again.

But what is charge? I said it’s the fundamental unit of electromagnetism, but what does that mean? It basically means that the charge of a particle or object describes the strength of its interactions with the electromagnetic field, in a very similar way to how mass describes the strength with which an object interacts with the gravitational field. In fact the equations for the force of gravity and the electrostatic force (the force between two stationary charged particles, also called the coulomb force) is basically the same. For gravity, the force of attraction is given by the equation F=G*m₁*m₂/r², where G is the gravitational constant, m₁ and m₂ are the masses of the two objects, and r is the distance between them. The electrostatic force of repulsion is given by the equation F=k_e*q₁*q₂/r². The only differences are that instead of the gravitational constant G, we’re using Coulomb’s constant k_e, and the electric charges of each of the two particles q₁ and q₂.

Current

Current is just the movement of charges. That’s it. Real simple. If you take electrons and flow them through a wire, you have current. Specifically, current is a measure of how quickly charge is moving. The common unit of current is an Amp, short for Ampere. Going back, we talked about the unit of charge milliamp-hours (mAh), which gives a clue as to what an amp is. An amp is a coulomb per second, which means a wire carrying a 1 amp current will have 1 coulomb worth of electrons moving past every point along the wire, every second. So a milliamp-hour means the amount of charge that flows over an hour with a current of 1 milliamp (one thousandth of an amp).

Magnetism

“But Switchy, this is electromagnetism, how does magnetism come into the picture?” Well sorry for keeping you waiting, I had to explain current first, and to explain current I had to explain charge. Magnetism, and specifically electromagnetism arises as a result of moving charges (current). As it turns out, any moving charged particle has a circular magnetic field around it:

Moving charge is just current, and this is how electromagnets work: make a loop of wire and pass a current through it and it will act as a magnetic dipole so long as the current is flowing:

Electromagnetic Induction

Kind of like how a moving charge (current) creates a magnetic field around it, a moving/changing magnetic field will create an electric field and try to induce a current if there are charges present. In general, the magnetic field doesn’t “want” to change. So if there are charges that can be moved so that an otherwise changing magnetic field stays the same, then those charges will experience a force that will cause them to move and form a current (if they are able to move freely) that creates a magnetic field that opposes the change.

There is so much more I want to talk about, and I’d love to go into much more depth, but I need to get some sleep. I’d love to yap about electrical potential/voltage, electromagnetic waves and their particle duality, the birth of quantum physics, etc. etc. But I also do have some goals in mind with these threads, and this is some basic background that combined with the magnet mega I made before, should lay much of the foundation to talk about electric motors and other cool stuff in a later mega.