 Let's say you take a neutral electroscope. Charge up a plastic rod with negative charge, then touch the rod with the electroscope. The leaf on the electroscope moves, but why does this happen? We can explain this movement by considering some attractive and repulsive forces between electrons and protons in the electroscope and rod. The electroscope starts off being neutral, which isn't to say it doesn't have any charge, but rather that it has equal amounts of positive and negative charge. I'll show that by putting in equal amounts of protons and electrons here on the electroscope. When the negative rod touches the electroscope, conduction occurs. Conduction occurs when there's contact between charged and neutral objects. This allows some of the electrons from the negative rod to move into the electroscope. Since the electroscope is made from metal, which is an electrical conductor, the electrons spread evenly throughout, including into the leaf of the electroscope, and the leaves repel due to the build-up of negative charge. Note how in conduction a negative rod causes the neutral electroscope to also become negatively charged. What if we try the same thing, but with a positive rod? In this case, electrons in the neutral electroscope will be attracted to the positive rod and will move from the electroscope to the rod. This leaves fewer electrons in the electroscope, meaning that there is now more protons than electrons remaining, and the electroscope is net positive. The leaves deflect again due to the repulsion between the protons left in the leaves. Note through this process, protons never move. It's only the electrons which are the moving carriers of charge. And also note how in conduction a positive rod caused a neutral electroscope to become positive. Interestingly, if you take that now positive electroscope and move the positive rod close to but do not touch the electroscope, you can make the leaves move even further. What's going on here? There's no conduction taking place. Moving a charged object close to but not touching another object is called induction. In this example, the positive rod will attract the few electrons left over in the electroscope and pull them up to the top of the electroscope. This is a temporary movement of the electrons called electron migration. The movement of the electrons away from the leaves mean that the leaves are even more positive than before. A larger positive charge means that the leaves repel each other more than before. A similar process can occur when a negative rod is brought close to but does not touch a positive electroscope. To understand this situation, you need to remember that even a positive object still has some negative charges within it. It's those negative charges that, when the negative rod is brought close to the top of the electroscope, repel away from the rod and migrate down into the leaves. This causes the leaves to be less positive overall, so we see the leaves moving slightly closer together. In a final experiment, we can also cause the neutral electroscope to gain a charge without ever touching it to the rod. This process is called induction and grounding. Here we bring a charged rod, in this case it's negative, close to the neutral electroscope. The electrons in the electroscope will repel away from the rod and migrate to the right side of the electroscope. If we ground that side of the electroscope by touching it with a wire attached to the earth or even with our finger, we can allow those electrons to move even further away from the rod and leave the electroscope completely. This leaves the electroscope with a positive charge and no tau in induction and grounding. A negative rod will end up giving us a positive electroscope. Of course the opposite scenario is also true. To practice this yourself, try and draw out what would happen if a positive rod was brought close to a neutral electroscope.