Friday, February 15, 2013

a lesson on charge, work, and energy

So, I'm thinking it's time for another physics lesson...and this time we're going with a bit of electricity.

Electricity and magnetism have never been my favorite--just ask Dr. Hemmati, my professor for that subject in undergrad!
   ~Don't get me wrong; I'm definitely a big fan of all the wonderful things we have because of electricity. I'm just not a big fan of all the crazy things behind it: Maxwell's equations, Poisson's equation, Laplace's equation...the list goes on, but I won't :0)

Honestly, though, I'm one of those rare physicists who would be perfectly content saying, "You flip the switch, magic happens, and the lights come on!"...which doesn't go over so well with professors.

This semester, though, I'm taking Classical Electrodynamics I, my first grad school electricity course. The professor is great and has this novel idea that he should teach us things (sadly a rare thing among way too many teachers...but I digress). And you know what? I think I may even be starting to understand some of this electricity stuff!

So, now for the physics lesson:

If you've ever played with magnets, I'm sure you've noticed that certain magnets push each other away while others pull together. That goes right along with one of the fundamental aspects of electricity--charge.

Everything in our world (and other worlds, but we'll go along with the ancient idea that we are the center of the universe for a moment and ignore everything else) is made up of tiny things. At one point the smallest of these things was thought to be the cell. Biology text books even went along with that for a while, saying the cell was the most simple, basic building block. Then, biologists discovered even tinier things inside cells that they called organelles--"little organs" because they do for the cell what our organs do for our bodies by processing and absorbing nutrients and eliminating waste (among a whole lot of other things).

Even those tiny organelles, though, are made up of an insane number of tinier things: proteins, polymers, lipids, and other molecules. It seems like no matter how small we get, there's always something smaller, something more fundamental.

This isn't supposed to be a biology lesson, though, so here's where the physics comes back in. Those tiny molecules, so small that we can't use light microscopes to see them, aren't the smallest we go. All those molecules are in turn made up of something even more fundamental--atoms. You know, like how a single water molecule is actually H2O, two hydrogens and one oxygen. What makes it even crazier is that those atoms can be broken down even more--into "subatomic particles" (physicists can be so uncreative with that whole naming thing) called neutrons, protons, and electrons.

This is where charge comes back into the picture (you figured I would get back around to it eventually, right?). Neutrons are neutral, hence the name. The ones we're interested in right now, then, are the protons and electrons.

Protons have a positive charge and electrons a negative one. In a way, they can be thought of kinda like tiny magnets. The big difference, though, is that while a single magnet has both a north and south pole (kind of like a positive side and a negative side), these subatomic particles don't. A proton is positive no matter which way you turn it.

So now we have this tiny thing, so small we look at it as a single point. If that point is always negative, that means that if we could break one of those points into tiny pieces all those pieces would have the same positive charge. So, like two north poles of two magnets, they would push each other apart.

If you've ever had the chance to play with any decently strong magnets, you've seen that it can be impossible to make them touch if they don't want to. Even little bitty magnets you can hold in your hand can be strong enough to keep even these guys from forcing them together:

So what in the world does that have to do with our little blown apart proton? Well, let's look at what would happen if we tried to gather all those little pieces back together to reassemble the single point charge. Starting with one piece, it wouldn't be a big deal to move it to where you wanted it. Once you move that second piece, though, things are going to get significantly harder. Now it's like you are pushing two matching poles of magnets together--and that takes some work.

Uh oh--now I've brought another physics concept into the story: work.
     I bet you're not even breaking a sweat yet, so we're still quite a ways from the obligatory physics panic attack, right? Good.

If you're going to do work, it's going to take some energy. For that, we'll go with the physicist's best friend: a big box sitting on the floor. We'll make it empty at first, and push it across the floor. Pretty easy, right? It doesn't take much work, so you don't have to use much energy. As we add a bunch of stuff to that box, though (you know, like all those books that you have stacked on the floor because they don't fit on the bookshelves...don't tell me that's just at my house...oops), it gets a bit harder to move.

You have to work harder, and that means you use up more energy. When you keep adding to the box, eventually it takes all your energy to move the thing.

The same thing is going on with our shattered proton. Moving that second piece in to meet up with the first takes work, therefore energy. When we move a third piece in it takes more because it is being pushed away by both of the others. This goes on for every piece: by the time we're trying to move the 576th tiny piece of that shattered proton in, it has 575 pieces pushing against it. That's going to take a crazy amount of work, which means a crazy amount of energy.

(Look at that! Charge, subatomic particles, work, and energy all without even making you start to hyperventilate!)

In fact, it takes so much energy to push all those pieces of that charge together that we can't count it. One point charge, then, has to use an infinite amount of "self energy" just to hold itself together.

Those atoms we were talking about earlier, like the hydrogen and oxygen ones that make up water? If we look at oxygen on the periodic table we see it has a big number 8 with it. That means it is made of 8 protons and 8 electrons (there are neutrons thrown in there, too, but we're not worried about them for the moment so we'll leave them out. Convenient, huh?) That means 8 tiny positive charges and 8 tiny negative charges, which doesn't seem too bad. After all, that just means 8 tiny north pole magnets to attract the 8 tiny south pole magnets.

The thing is, though, the 8 positive charges are essentially all stuck together while the 8 negative charges fly around them. In the nucleus, then, where those 8 positive charges are stuck together, we are dealing with an infinite amount of self energy at least 8 times. More if you think about it, because we're also dealing with the energy it takes to hold those 8 positive charges to each other.

Look around you for a minute. Everything you see (including yourself) and everything you don't see (like the air) is dealing with this right now: infinite amounts of energy, all of it wanting to go back to being relaxed and not doing any work. It's true--in that sense atoms are like people and would rather be relaxing than working.

The crazy thing is, physicists don't really know what keeps everything held together, keeps those tiny charges from releasing the infinite amount of energy it takes to hold them together and simply blowing everything up.
There's a field in physics trying to figure that out right now, studying these things called "quarks" (I guess physicists get creative with naming every once in a while after all) that are thought to be what subatomic particles are made out of...
but you know what?
I'm just glad that that "infinite" amount of energy and the "infinite" power it represents is nothing compared to the power of the One who spoke all of it into existence.

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