10.2 Insulators and Conductors

In this lesson, we're going to look at some more theory in terms of electrostatics. The first one is we're going to try to figure out what's the difference between insulators and conductors and look at some specific types of conductors. First off, let's realize that there are actually four categories. It's not just insulators and conductors. We actually have insulators, and we have different levels of conductors. Something that's sort of a conductor but not quite is the semiconductor. And then, at the end, one that's an awesome conductor is a superconductor. Let's go through what they are quickly before we get into some equations or formulas and so on. First off, it says imagine we've got two metal spheres; one charged and the other neutral. So let's suppose we have something with the negative three. Charge like three electrons and let's suppose we have a neutral metal. So, what it's saying is, if we put an iron nail between them, and touch them together with metal, what will happen is: I'm going to change this one so it's a little bit better. Let's suppose we have four electrons in the first one. We touch the two spheres together with an iron metal, because iron is a conductor. We should get two of the electrons moving to balance things out. So, we would then end up with two electrons in each metal sphere. This would give each other a net charge of negative two. But if we would have done the exact same thing, but used a rubber rod, so if we had our four electrons in the original and zero in the other. In this case, we put a rubber rod in between. The rubber being an insulator... It's not likely to move any electrons, so nothing would change. The idea is that in general, most metals are good conductors. They allow electrons to move freely. On the other hand, most other materials are insulators. Keep in mind that even the weakest insulator or the weakest conductor still allows some sort of charge to pass through, although usually not enough to make any difference. Now, let's figure out what a semiconductor is. A semiconductor is, as we go back to our chart, in between an insulator and a conductor. It's sort of like being halfway in between. There are certain kinds of materials that we classify as semiconductors. Silicon, germanium, carbon, and selenium are all examples of elements that we consider as semiconductors. Each one has its own unique properties. Different properties can make a substance act as a conductor or an insulator. One example is silicon, which is used in computer parts and chips. Depending on the temperature, silicon can either conduct or insulate electricity. Temperature plays a crucial role in determining conductivity in many cases. Another interesting substance is selenium, which acts as a conductor only in the presence of light. In dark conditions, selenium functions as an insulator. This property of selenium is utilized in photocopiers, where the drum is made of selenium. When the light is turned on during the photocopying process, selenium becomes a conductor, allowing the toner to stick to the drum. To wherever the letters are and make your coffee. Where, if it's dark, it skips. It's kind of cool how things like that can work for certain applications. Another name that we use for semiconductors, sometimes, it's called a metalloid. You might see or hear that, and a metalloid just sort of means sort of a metal. So, we'd say selenium has a metalloid because it works in some conditions, in others. Our last one that's on the chart is a superconductor, and these typically are what we classify as, you know, almost perfect or terrific conductors that basically lose no energy. So, in any kind of electricity transfer, we usually lose energy along the way. So, when you plug in your extension cords to charge your iPhone, for example, the electricity coming out of the wall, as it goes down the cord, it loses less and less due to friction and heat, and whatever. So, by the time it gets to your phone, there's actually some electricity. That gets lost. Some of that transfer energy is gone, and the same thing happens in a powerline. So when our power goes from F chord to our house, it loses some along the way, okay? So a superconductor, basically the idea is, nothing gets lost. Pretty much all the energy passes perfectly through the conductor. The negatives to superconductors is that they typically only work when it's super cold, when it's near absolute zero, which would be zero degrees Kelvin or minus 273 Celsius. Recently, though, they're starting to make ceramic superconductors, as they're sort of made out of ceramic tile-type material, and they work well in about the minus 200 range, which is about the temperature of liquid nitrogen, which is way more practical and more affordable. So they're starting to use more of those kinds of things for the superconductivity-type applications would be, you know, things like super high-end NASA spaceship kind of things or computer. Servers and high-end applications typically don't deal much with superconductors. But in the real world, we often encounter the question of why some things conduct electricity while others do not. Why do conductors work better than insulators? To understand this, we need to look at how things work at the atomic level. Remember that in an atom, we have electrons orbiting the nucleus. Some of these electrons are located far beyond the nucleus and are free to move around. In conductors, these electrons are relatively loosely bound to the nucleus. On the other hand, in insulators, the electrons are tightly bound to the nucleus. This is often explained as there being weak bonds between the nucleus and electrons in insulators, making it easier to remove those electrons. Away or add them in an insulator, we think of the electrons not necessarily being closer but having a stronger bond to the nucleus. So we can't get those electrons to move away as freely. That's kind of the key idea. And remember, it's the electrons that are moving, not the protons. The protons in the nucleus are tightly packed; they're pretty solid. It's pretty tough to get those protons to leave the nucleus. It's only the electrons that we can add or take away. So we're gonna go through some basic diagrams today, and in the next lesson, we'll include a little star to help you visualize what's going on here. The first thing we're going to look at is what happens when we have a positively charged object move towards something neutral. In this case, our rod is positively charged as we get it closer and closer to something neutral. What happens is, all the electrons in a neutral object remember. In the neutral object, we have our positives and electrons. Let's assume they're fairly evenly spaced throughout the entire metal. Okay, so we have sort of an equal balance. But what happens is, as soon as we bring something positive close to it, most of the electrons are free to move. They're going to pile up on the end that's closest to that positive object. So it's not like the protons are getting pushed away, alright? They're still going to be positives over here. So maybe this diagram isn't too accurate, but you know, so our positives are equally spread out throughout the whole thing. Let me just kind of finish off this diagram. So let's suppose that's our spread of neutral items. So the positives will stay there, but what's going to happen is all of those negatives, the electrons. The ones that are way over on the far end are going to move to the cosine, so the electrons will move. In essence, it would make this negative and leave the other end positive because there are no more electrons there. Okay, so what we do is we call that a charge separation. Even though it's one object and it's still neutral, the charges have separated. The electrons have all piled up on one end, making one end negative and the other end positive. The same thing would happen in reverse when we bring a negatively charged rod. So this rod that's negatively charged comes close, and what it's going to do is reverse. It's going to chase all the electrons away, so all the electrons pile up on one end, leaving the other end just positive, which will create charge separation once again. Lastly, just in order to kind of keep it an idea if it was an insulator. So if we looked at that last example I was showing you conductors, so if these were Insulators, those blocks of objects, look like they do not allow movement of negatives. They are tightly packed, so the negatives are not free to move. If we bring a positively or negatively charged object close to an insulator, nothing or very little will move. This lack of movement is not enough to make a noticeable difference. On the other hand, in the case of a semiconductor, only a few electrons can move, and the number of moving electrons depends on different conditions. For example, if it is cold, there may be a few more electrons that will move, while in warmer conditions, fewer electrons will move. In the case of insulators, none of the electrons can move. Therefore, when we bring a charged object close to an insulator, nothing happens, and that's the end of the story.