Charging by Induction
Charging by Induction
In induction a neutral conductive material, such as a sphere, can become charged by a positively or negatively charged object, such as a rod. Here we have our sphere which has a neutral charge right now, so it has the same amount of electrons and protons, and then here we have a rod.
We’re going to say that this rod has a positive charge (I’m going to put some plus signs here showing it has a positive charge). At first there’s not really an activity, but once this rod is brought closely to the sphere—notice it doesn’t touch the sphere but it gets very close—what’s going to happen is all the electrons are going to come over here to this side of the sphere because they’re attracted to the rod, and then you’ll have the positive charges over here.
Now about this time a ground touches the sphere, so basically, this is (this could be) someone’s finger touching the sphere, and then they’re touching the ground, so they’re connected to the ground. (I’m just going to write here that the ground touches it instead of trying to draw someone’s finger).
As soon as this outside source actually touches the sphere, electrons are going to flow into the sphere. What’s happening here is that all the electrons that are already in the sphere are attracted to this rod, so the electrons that are in the person’s finger are also going to travel into the sphere, because they also want to come over here and be near the rod.
Now, say we had a similar scenario, we have a sphere again and a rod but this time it has a negative charge. What’s going to happen is, positive charges are going to be over here because they’re attracted to the rod. Then all the negative charges are going to be over here because like charges repel each other.
We have negative charges here, and negative charges here—so these negative charges want to get as far away as possible. Now we have a ground touching the sphere, so these electrons are going to travel into the ground. They’re going to travel to this outside source, so they can get even farther away from this negatively charged rod.
Notice here what happened is more electrons went in, so now there was more electrons than protons, so now this sphere has a negative charge because electrons have a negative charge. Now over here electrons moved out, so now there’s less negative charges—there’s more positive charges, which gives this a positive charge.
What you can notice here when you charge by induction, the sphere is going to end up with the charge opposite of that of the outside source. Here a positive charge came in, but the sphere ended up being negative. Here we had (a positive, excuse me) a negative rod, but the sphere ended up with a positive charge. The charge is always going to be opposite that of the charging rod.