Science In Real Life

Electricity. We all use it everyday in our homes and out on the town. So much of our daily lives is made possible by electricity that it is easy to forget just how thoroughly it permeates the way our world works. So I’m going to explain to you how it works. Now, electricity and magnetism are so intimately connected that in some ways even thinking of them as distinct phenomena is misleading. So I’m going to do a two-part essay in which I shed some light on both subjects.

We’ll start at the beginning, ignoring the fact that it is technically impossible to start anywhere else. Matter is made of atoms, with a nucleus at the center. Positively charged protons and neutral neutrons (we physicists are really lazy about naming things) are squished together in the nucleus. Around the nucleus flit negatively charged electrons, and the more astute of you have already figured out which one is responsible for electricity. Opposites attract, so normally the nucleus holds onto its electrons like a scared roller coaster rider holds onto the bar. But on the outskirts of the atom, the effect of the nucleus is minimized, and so in some materials atoms will shed their outer electrons if you so much as look at them funny. These materials are called conductors, and most metals fall into this category.

The term “electricity” is a very broad one; it can be used to refer to half a dozen more specific phenomena, like charge, voltage or potential, field, or current. Electrons and protons have charge. What we’re usually concerned with is current, the flow of charge. It could be positive, or negative; if charge is moving then we have an electric current. For most applications, as it turns out, the two are indistinguishable. Imagine a whole bunch of electrons lined up in a row. Now the rightmost electron shifts to the right, and leaves a space. Then the next one follows, and so on. Take a look at the diagram.

(Source: MS Paint! Gotta love the high art here at Science In Real Life)

You can either say that the negatively charged electrons are moving to the right, or you can say that a positively charged “space” is moving to the left. As long as we don’t care about the direction of the current, it can be considered either positive or negative. In fact, physicists didn’t definitively know which of the two charges was moving until something called the Hall effect demonstrated it in 1879. As it turns out, it’s electrons that do the moving most of the time (nuclei are heavy and hard to move), so we, uh, elect to name electrons after electricity.

So we have copper wires conducting current. There are two types of current in our devices,  Alternating Current and Direct Current (Australian rock bands notwithstanding). The difference is pretty much exactly what it sounds like. Direct current is a continuous flow in one direction, and alternating current jumps back and forth between directions like an indecisive politician. Power companies set it to do this fifty or sixty times per second (depending where you are in the world), so the fluctuations in any appliance are far too rapid for the human eye to detect. In the USA at least, all outlet power is AC, and any devices that require DC will have a converter.

It is important to note here that the physical movement of charges is not the key mechanism of an electrical current. Think of it more as analogous to setting up a bunch of dominoes and then having each one knock the next down. Like a disturbance in the Force, a disturbance in their position travels much faster than the actual particles do. For alternating current especially, you can imagine the current as a very long, very microscopic version of one of those Newton’s Cradles, with an impulse traveling back and forth between the ends of an essentially static lineup.

Static electricity is a related phenomenon. One of the simplest ways to produce an excess of electric charges is via friction. Take a latex balloon, rub it in your friend’s hair, and watch the ‘do stand on end. Whether or not this person is still your friend may vary. The latex in the balloon grabs electrons off of the strands of hair. All the strands of hair now have an excess positive charge, so they repel away from each other.

In winter, static charges more easily build up. Why? Water conducts electricity (more accurately, minerals dissolved in water conduct electricity), so when there is more humidity, static charges dissipate easily through microscopic water droplets. When the air is dry, as in winter, the excess charge has nowhere to go, like a dork on prom night. When a conductive object gets close enough, the charge will jump the gap in what’s called a spark.

What’s their motivation to jump? It’s not people on the street yelling at them to just do it already. There’s a concept physicist use called electrostatic potential. Let’s say I have a metal sphere with a bunch of extra electrons on it. Since the electrons all have the same charge, they are repelling each other. Like Elvis impersonators, they like to work solo. So now I bring over another metal sphere, this one a clean slate. There happens to be an electron on the first sphere closest to the second one. All the other electrons on the first sphere are pushing that one away as hard as they can. That “push” is the potential. Whether or not it jumps is simply a question of whether or not the push is strong enough to get it across the distance it is facing. Reducing the distance or increasing the push will increase the likelihood of a spark, which is why you can shuffle your stockinged feet on the carpet all you want, but you won’t get a spark until you touch a doorknob or your little brother’s head.

This is the effect responsible for lightning, but frankly that’s a column all to itself. So I’ll leave it here. Tune in next time to find out how electricity relates to magnetism!