Conventional current

When we start to study electricity, we need to get an idea of what is current and what is voltage. In two earlier videos, I talked about the idea of current and voltage, current and voltage, and what they meant. When we talked about current, it's easiest to describe current when we talk about wires. Let's say we have a copper wire. We talked about a copper wire, and inside it, there were electrons in it, and they have a negative charge. We know they have a negative charge.

If we put a voltage on them, those electrons would move in some direction, like that. So, if I put a plus voltage over here and a minus voltage over here, the electrons are repelled by the minus voltage, and they're attracted to the positive voltage. That is called an electron current.

So, talking about current in terms of what's actually happening inside a wire makes some sense; it's easy to understand current and that these electrons are moving around. Whenever we talk about this, we'll talk about it specifically that there's an electron current going on here.

Now, at the same time, what I said in that video, and I'll say again, is the convention for describing current. This is called the conventional current direction. The convention we've had for hundreds of years is that current is the direction that a positive charge would move if there was a positive charge there. So, whenever we talk about current from now on, it'll always be conventional current.

In fact, we don't even need to mention conventional anymore; it’s just current. Current is the direction that positive charges would move. If we ever talk about electron current, then we'll use the word electron current.

Now, as a reminder, when we talked about voltage, this was built up by analogy. The analogy was to electrons rolling down a mountain top. So, here's our mountain. Remember this? I built a battery or another voltage source like this, and we said that what a battery does is it pumps out energy to electrons, and they go down a hill, roll down hill, and go back into the positive terminal of the battery.

When we design circuits, what we do is we put stuff in the way of this electron on its path, and this is where we build our circuits. So, the electron current is going in this direction here, down the hill. The conventional current direction, or the current direction, is this way.

So now, I'm going to redraw my circuit and my battery. I'm going to flip the battery around until the positive terminal is on the top, and I'll put my circuit over on the side over here like this. There's my circuit that I just built. Let's connect those circuits up like that.

This is the plus side of the battery; this is the minus side. The plus side goes with the long bar, and the minus side goes with the short bar there, and the current direction here, the conventional current direction, or just plain current direction, is in that direction, out of the positive and back into the negative.

From now on, this is what we mean by current, and we know that the electrons are in here; they're heading around this way, like that. But that's okay. This is the nomenclature for conventional current or just plain current.