10.1 Electrostatics

Okay, today we're gonna go through a little bit of history and some basics to sort of understand how the idea of electricity was developed. And the first topic we're going to look at is static electricity. We've probably heard stories over the years saying that Benjamin Franklin was flying a kite during a lightning storm, so he discovered electricity. Or Thomas Edison invented the light bulb, so he must have invented electricity. Or Alessandro Volta made the first battery. Or Nikola Tesla made alternating current. And the list goes on and on. All of these people helped harness energy and use electricity, but they never eventually discovered electricity. The first mention that we know of, by a written account, is the Greeks. So back in like 600 BC, the Greeks found static electricity to be more of this sort of something that was cool or amusing. They would rub a chunk of Amber, which is just a hardened SAP, is a yellow kind of thing. It looks like the mosquito things on Jurassic Park—that's amber. So, they would take that thing, webbed with fur or something, and then notice that it would become statically charged. They would be able to pick up dust, leaves, anything like that. What they saw, what they experimented with, is what today we call static electricity. They had no scientific explanation or rationale behind it; they just thought it was interesting. But what they did realize is that if they would charge two objects by rubbing two pieces, sometimes they would get them to repel. So, if they took two chunks of amber, rubbed them both, and mixed each other, they would separate on their own. This is electricity and static electricity, as we're gonna see in a few minutes. Later on, in the middle ages, this sort of moved them quite a bit ahead. In the 1600s, now William. Gilbert was a guy who tried to make sense of electricity and static electricity, which the Greeks had described. He wanted to come up with some theories, and he was actually the first one to coin the word "electric." It is basically just a variation of the Greek word they used for amber. That's how that came about. He had some sort of success, but his key idea was that magnetism and electricity are different. Up until that point, most scientists thought they were the same thing, just different versions of each other. But he said that a magnet is always a magnet. Once you have a magnetic piece of iron, it will always attract particles. However, with electricity, we had to rub the amber rod to create an electric static charge, and eventually, it would wear off, whereas the magnet would not later on. Now, in the 1700s, Benjamin Franklin is... this is about the time when he started. Getting involved, and according to the stories, he did indeed fly a kite. But he didn't fly it on a lightning day. He was just trying to figure out if there's any kind of electric charge in the air. Others have done that, so their scientists tried to fly their kite on a lightning rod in a lightning storm, but they all were killed. Another interesting story is that Franklin typically would get his son to do all the experiments while he just stood back and watched. So even if there was some sort of mistake, it probably would have been his kid that got killed and not him. Anyhow, what Franklin did find out was that electricity is basically just a discharge of static electricity. And then he was the first to start coming up with the ideas of positive and negatives, and so on. So he would take a chunk of amber and he would charge it. He'd have it hanging from a thread from the ceiling so that there was nothing touching it, and he would charge another piece of amber on. Would move it close to it, and he would get them to repel or move away from each other. Then he found that if he rubbed a glass rod with silk, it would do the same thing. So, you'd have a glass rod hanging there, he'd rub it, put a charge on it, grab another one, put it close together, and they would also repel. But then he found if he put the amber rod and the glass rod near each other, they would attract. So, he found that the amber ones repelled, the two glass rods repelled, and each attracted. So, he figured the charges must be different. And he just decided, for no particular reason, just to come up with a name. And he knew that to be opposites, he said the glass one was positive and the amber rod was negative. They could have been the other way around, it could be something totally different, but that's what he went with, and that's what's pretty much stuck ever since. He also tried to come up with the idea of why there were these positives and negatives and attracting and repelling kind of ideas and his theory which isn't accepted today, but it kind of was the basis for what we do use. He sort of thought that every object is made up of a fluid, and he called it an electric fluid. He thought that everybody's electric fluid was positively charged, and if you had too much of it, then you were positive overall. If you had not enough, then you were negative. So he sort of used this idea that you should have a certain amount to be neutral. Anything more was positive and anything less was negative. He backed it up with sort of seeing that you could charge an object. You could create a charge on one, and then what that showed was a deficit on the other. So he sort of came up with the idea that if you rub a balloon on your hair, you are removing electrons from your hair to the balloon or vice versa. So one becomes positively charged and one becomes negatively charged, but the balance was still the same. And that was kind of the key idea to his fluid theory. Balance: I was always the same. We're just shuffling from one to the other. So, although that's not right, we did it. It did lead to what we use today, which is the law of conservation of charge. This means the net amount of all electric charge produced is always going to be zero. So, we can have positive and negative interactions, electrons moving back and forth. But the idea is that the total net result is still going to be zero. So, we can't create or destroy charge. All we can do is move them around. Since that time, in the last hundred years or so, it's now pretty much accepted knowledge that it's not based on some sort of fluid. It's based upon the makeup of the atom. We know that our nucleus is made up of protons and neutrons. The protons are positive and it's surrounded by electrons in orbit. In the normal state, the protons and electrons balance out, so we end up with a neutral charge. But we also know That we can add or gain or lose electrons from the atoms, which would then create an ion. So, if we lose electrons, it's going to be positively charged. If we gain electrons, it's going to be negatively charged, and so on. One quick question or one thing to think about is, normally when we get static electricity, it only seems to last for a while. So, if we rub our hair on a balloon and stick it to the wall, we wait, it might last an hour or two, but it might not last too long and eventually it falls off. So, the question is, where does that charge go? It doesn't just disappear. We already say that the total charge can't be created or destroyed, it just gets shifted around. So, what ends up happening typically with static electricity is, the excess charge leaks off into water molecules. So, for example, if you have excess electrons, those electrons are going to get attracted to water molecules, which typically are positive on one side and negative on the other. So, they start to sort of cling. Collecting on the positive end of the water molecules, so eventually the object will lose charge and become neutral over time. It's also sort of the idea of grounding, right? If you have a grounding rod or you touch something, it will balance it out. That's why when you shuffle your feet on carpet and you touch a doorknob or whatever, it'll spark. That's basically just the excess charge leaking off or neutralizing. In terms of water molecules absorbing charge, it's sort of neat that we typically get more static. In turn, if the air is drier, there isn't enough moisture, so the electrons aren't picked up as often. Therefore, we tend to get a little more static in the wintertime. And that's it for the theory. There's not much in terms of calculations or anything. We're gonna get to that in the next couple lessons.