 Okay, so we're going to start off by reviewing a little bit of what we've seen already in chapter 24. This is going to highlight things you should already know, but we just want to make sure that we've got all of these things sort of highlighted in terms of what we need to be focusing on today. So we've been working in chapter 24, which is Gauss's Law, and in that we had two major forms for finding the flocks, and this is our symbol for flocks. In one case, we're integrating over a surface, and we have to look at the dot product between the electric field and the incremental little areas. And this could be a very messy quantity in general. Then we had Gauss's Law, which let us know that that flux could be more simply calculated if I know the amount of charge inside that surface over the constant epsilon naught. And epsilon naught is our 8.85 e to the minus 12 Coulomb squared per Newton meter squared. You should have that written down in your notes somewhere. It's going to come back up on a later slide, so if you haven't gotten it written down completely yet, just hold on, you're going to see it again. Now the useful thing about Gauss's Law was if we have both of these forms, we could actually equate both sides here. And if the symmetry is just right, then this integral becomes much easier and becomes just e times the Gaussian area. And we talked last time about what makes that symmetry just right. If you do have that just right symmetry, though, you can use it to find the electric field on your Gaussian surface. You have to know how much charge is inside your Gaussian surface. You still have to use your epsilon naught, and you have to know the area of the Gaussian surface that actually has electric field going through it. Now let's review the units, because some of you guys have been messing up on that. If I've got my basic electric flux, it's going to be the electric field times the area. Electric field has units of Newton's per Coulomb. Remember it was a force per charge. An area should have units of meter squared. So that means flux should be Newton meter squared per Coulomb. And we should get the same Newton meter squared per Coulomb, even if we're using the other form of Gauss's law. Now in order to do that, you have to take into account what units do we expect on charge. It's going to be Coulombs. It might be micro-Coulombs or nano-Coulombs, but Coulomb is the base unit there. You just need to remember to put in your metric prefix. And here again is your epsilon naught, the 8.85 e to the minus 12th Coulomb squared per Newton meter squared. I'm going to leave this slide up here for just a little bit before the end of the video. You need to make sure you have this constant written down. And then you're going to answer a couple of other things on the paper in regard to working out some units. Got it written down? Okay, here we go.