 So we're almost ready to move on to the back side of the worksheet here, but before we actually get into that I want to show you some information that's going to help you understand these conceptual questions here at the top of the Backside of the worksheet, and I'm going to do that using one of the tools that we have for our Blackboard links and just to pull down so you can see the website here. This is the PHET the physics technology thing out of the University of Colorado. So I've got a field here, and I've got little charges that I can place out there. And I can make this as complicated as I want throwing all sorts of charges in there, and it can be kind of fun seeing how you can get all this to work. But this visualization method uses what we call a vector field. So at every point on the grid it's going to give you a little arrow showing you the direction of the field. It doesn't exactly show you the strength of the field, but depending on how strong the coloration of the arrow is, white is a very strong field and where it fades out is a weaker field. So let's go back and look at a little bit simpler situation. Let's say I have a single positive charge. Now we're already seeing the directions that we expect based on what we saw in our previous stuff. You can already pick up a little bit here, but we also have these little sensors. Now I can place these sensors somewhere out there, and it gives me an indication of how strong the field is by how long that arrow is. Now I can move these around, but I can also just grab extra sensors to be able to compare things. So I can have a sensor over here where it's very far away. Hmm. Can't even really see that arrow. I can have a sensor a little bit closer in. Oh, I just see the red tip of that, or I can have a sensor that's even a little bit closer here. So we can start to see a pattern, and I'm going to try not to overlap these, for how strong the field is at different points around there. So if you're looking at your worksheet, the first question asked about a single isolated positive charge, and you're given three choices. Reading that question, looking at these arrows, it should be pretty obvious which one is the correct choice. Now, I'm going to go ahead and get rid of my positive charge. Oh, no sensors. And put in a negative charge. Now, the first thing you see is that the arrows have switched direction. And in this case, it almost looks like the arrow is pointed out, but it's just the arrow is so long it's going right through it. So what we've got here is you've got sensors and you've got the field. So we have the same sort of pattern here with the field strength out here versus the field strength in here. And if I get rid of this one that's really close, which is hard to see, I can imagine I could switch out a positive charge, get a field about that long, switch it out to a negative charge, got a field about that long, and you can sort of compare the strength of the two fields. You can also think about it in terms of the equation that we'll look at here in a minute, but was also included in some of the pre lectures. So here you've got information about the electric field. Now when I say larger and smaller, that's about the magnitude. And on these ones, I'm saying it's the same magnitude, but then looking at the direction. So if you're not quite sure yet, you might want to go back and play around with the tool. You can even add in values, although it uses a different unit system than we do, to try and get an estimate for what's going to happen for positive charge or a negative charge.