 Hello, my name is Brad Langdell. I'm here to talk to you today about charge particles in uniform electric fields This is a little procedure I call getting the big V from the little V or the little V from the big V depends on which way you're working Here's what the question looks like So you've got a particle it's got a charge in this case is an electron. It's released in a pair of parallel plates Okay, so these parallel plates are going to provide a uniform electric field They're going to accelerate the particle so the electrons released from the negative parallel plate and it accelerates to the other plate When it does this it moves through 15 volts potential difference Okay, this is the kind of the energy per unit of charge is going to gain What speed does the electron reach when it hits the positive plate? Here's the steps are going to go through Okay, first step like in any good physics problem. You're going to draw and label a diagram. Here's the basic idea So we've got a negative plate or positive plate. We've got an electric field going to the left Electric fields go away from positive charges towards negative charges And then we've got the electric force on this particle going to the right because the negative particles repelled from the negative plate Attracted to the positive plate if you look to a multimeter up across this the voltmeter function and tell you it's 15 volts All right. Now. What the heck does this 15 volts really mean? Well, you got to remember that voltage is Energy per unit of charge. I think that's a really kind of key thing to remember here energy per unit of charge Because if you know that this is energy per unit of charge then you can start thinking about the formula that you've got for potential difference and Understand that basically if you get the charge of this particle, you can just find how much energy it has and from there You can do lots of different things So I make a list of all the variables I'm given in the question I got the potential difference and then I also know the charge and mass of this particle The charge is 1.6 times 10 to the negative 19 coulombs as the elementary charge and the mass That's actually the mass of a proton. So we'll go in and change that it's 9.11 times 10 to the negative 31 kilograms that's the mass of an electron and Those are both in your data sheet so you can look those up when you need to now if you knew the mass a primary if you knew the charge and you knew the Potential difference then you can go through and solve for the energy and if you know the energy change That could turn into kinetic energy, which is exactly what's going to happen here The stored energy in this particle is going to be released as kinetic energy making it speed up So I can do a two-step calculation First of all finding the change in energy then making that energy equal to the EK and solve for the speed Here's what that calculation is going to look like So the energy gained by the electron now is going to go and change into Kinetic energy and to speed so I put in my 15 volts. I put in my charge Get my energy gained by this particle Then I can substitute that energy in for EK and then go through and solve for the speed I'm getting speed of 2.3 times 10 to this negative positive six meters per second So I started off by being given big V potential difference in the question and I also knew the mass and charge from the data sheet and I could get the small V speed out of that This is a really common calculation great one to know for your physics 30