### Video Transcript

An electron is accelerated across the potential difference of negative seven volts. The electron moves in a vacuum. What is the kinetic energy in electron volts of the electron once it has crossed this potential difference?

To answer this, we’re going to have to recall the definition of an electron volt. An electron volt is the energy involved in moving one electron through one volt of potential difference. If we were to see this in the form of an equation, it would look like this. One electron volt is equal to the charge of one electron times one volt. So we can see why it’s called the electron volt. It’s one electron through one volt. The reason that we have the electric charge of the electron here is because the product of an electric charge and a potential difference is how you get units of energy.

But hold on here! Don’t we know that electrons have a negative charge? If so, shouldn’t we be getting negative one electron volt? Well, for energy, this isn’t something we have to worry about, since energy always has to be a positive value. A way that we can represent this is by taking the absolute value of the product of the electric charge and potential difference. After we take the product of whatever it is in between these two lines, we just make it positive.

With all of this in mind, let’s look back at the problem. We have a single electron, which means that we only have the charge of one electron, that is being accelerated across the potential difference of negative seven volts. So all we have to do to find the kinetic energy of this electron in electron volts is take the product of the charge of an electron with negative seven volts, which would just be one times negative seven. But we need to make sure the value of energy is positive. So let’s take the absolute value too. This gives us a result of seven electron volts. So the kinetic energy of one electron moving through a potential difference of negative seven volts is seven electron volts.