 Now we can take a look at our worksheet. Now I'm going to refer you back to the previous videos because I'm not going to go over every detail of this as we work on the worksheet. So if something seems confusing, you might want to go back and watch one of the other videos. On the front side of our worksheet, we have a section labeled Electric Fields and Forces, and we've got two questions there. Now you may want to go ahead and look at your worksheet at this point rather than trying to read the questions on the video because it's going to be a little bit hard to see all the details. So in the first question, it says calculate the force acting on a four micro coulomb charged object in a field of 15,000 Newtons per coulomb. So I've got a little empty workspace over here, and I'm just going to go ahead and make note of a few equations. So first off, our basic equation relating electric fields and forces is that the electric field is defined as the force per charge, and it can be the test charge or it can just be the charge of the object experiencing that particular field or force. But in our problem, we're solving for the force, so we have to rearrange that. Now Algebra Review, you've got the Q on the bottom, so you need to multiply both sides by Q, and that will rearrange to give us our equation that the force is equal to the charge times the electric field. So now we got to figure out exactly what values we're plugging into this because we're solving for force. So over here, we've got a four micro coulomb charge, an electric field of 15,000 Newtons per coulomb. So if I were to write out those gnomes, I've got four micro coulombs. But I want to remind you, and you'll get in the habit of doing this pretty soon, that micro means e to the minus 6. It's a metric prefix, so you want to go ahead and write that out. And then our electric field is just 15,000 Newtons per coulomb. So now you can just plug those two values into the equation. Multiply the charge by the electric field. Now I'll just really quickly make a note here that I've got coulombs here and coulombs on the bottom that will cancel out. So when you get finished with your problem, you should have the unit you expect for force. And make sure you don't forget the unit as you're filling out your worksheet. I'll let you plug the numbers in yourself, and I'm not going to tell you what the answer is right now. Now we continue on to the second question here. If a particle feels a force of 15 Newtons to the right in a region with a uniform field of 30,000 Newtons per coulomb to the left, what is the charge on the particle? So in this case, we still start with our same basic equation that defines the electric field compared to the force per charge. But now we're solving for the charge. So we're going to have to do some cross multiplication here. And when you do that, you come up with the equation that the charge is equal to the force divided by the electric field. And in this problem, it gives us information about to the right or to the left. So we want to think of these in terms of vector quantities. And to the right and the left in terms of our vector quantities means we've got plus i hat or minus i hat. So combining those directions as well as the information given in the problem, we end up recognizing that my force is plus i hat. My field is minus i hat. Now right there that should tell you something based on what we've seen in previous videos about the sign of the charge. But even if it's not intuitively obvious to you, when you go through and plug your numbers in, you're going to see something about the sign of the charge. Remember, charges are either positive or negative. I'm also going to remind you very quickly that when we set up our equation like this, the i hats will cancel out. The Newtons were canceled out, but that leaves one over one over Coulombs in terms of our unit. And so when we've got that fraction on the bottom, it's going to invert. And that should give us the standard unit we expect for a charge. And again, I'm going to let you go ahead and do that calculation on your own. Make sure you write it on the worksheet. Make sure it's clear what the unit is and whether it's a positive charge or a negative charge.