Week 2, 9/11: Electricity

ἢλεκτρον μαγνήτης

There are four forces that govern everything in the universe: gravity, electromagnetism, and the strong and weak nuclear forces. We'll focus on electromagnetism, which is the law of opposites attracting. The force gets its name from the Greeks, who noticed the peculiar behavior of both amber and iron. Amber— translucent, golden stones of fossilized tree resin— has a more negative charge than the human hand. The friction of rubbing two opposite-charge materials together produces static electricity: valence electrons will jump from amber to finger, building up until released as a spark. Static electricity can cause super-charged surfaces to attract and repel each other (like balloons towards walls, or hairs away from each other). Iron molecules align into poles, which produces the magnetic behavior of iron attracting and repelling itself. The Greek words above, "elektron magnetes", come from the names and stories of amber (Phaeton and Helios), and the Magnetes tribe.

This a diagram of a copper atom. Copper is the 29th element in the periodic table, meaning it has 29 protons and electrons. Electrons orbit the nucleus of an atom in something more akin to a cloud, but we talk about them as shells of varying energy levels. The electron capacity for each shell equals twice the Principal Quantum Number squared. The Principal Quantum Number is both the energy level and the ordinal number of the shell. The innermost shell has a capacity of 2 electrons (2*1^2), the second has 8 (2*2^2), and so on. Because 29 is a number that leaves a lone electron in the outer shell, copper is a very conductive element. That outer, valence electron is easily passed in an electric circuit, which is why most wires are made of copper.

The metrics for each circuit are determined by the chemical composition and sequencing of components. Order doesn't matter for every component in every circuit, but these three metrics— voltage, current, and resistance— must be balanced with every component in consideration. It takes the energy of one volt to move a current of one amp through a resistance of one ohm. Because the units are related to each other in this way, the energy of a circuit can be expressed through an equation known as Ohm's Law: V = I*R, where V is voltage, I is current, and R is resistance.

When we talk about directionality in a circuit, there are a few confusing subtleties. If you're already confused, please skip this paragraph and just remember that current flows from the positive to the negative in a circuit. It's much more common to talk about the flow of current than the flow of electrons, and they're actually moving in opposite directions. Every component has two or more electrodes— the wire terminals that allow you to solder things together. With components that only allow the flow of electricity in one direction, the electrode that collects current is called the anode, and the electrode that emits current is called the cathode. Here's the confusing part: in a battery, the anode is the negative terminal where electrons flow out and current flows in; in an LED, the anode is the positive terminal where electrons flow out and current flows in. The difference comes from the former being a generator and the latter being an emitter.