If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains ***.kastatic.org** and ***.kasandbox.org** are unblocked.

Main content

Current time:0:00Total duration:3:57

- [Voiceover] When we
start to study electricity, we need to get an idea of what is Current and what is Voltage and in two earlier videos, I talked about the idea
of current and voltage, current and voltage and,
and what they meant. And 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 was, there was electrons in it, and they have a negative charge, we know they have a negative charge, and 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 easier
to understand current and that these electrons are moving around. And 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 is this. 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, and in fact, we don't even need to mention conventional any more, 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, uh, this was built up by analogy and the analogy was to electrons
rolling down a mountaintop, so here's our mountain, remember this? And I built a battery or another
voltage source like this, and we said, that what
a battery does is it pumps out energetic electrons, and they go down a hill. Roll downhill and go back into the, back into the positive
terminal of the battery. And when we design
circuits, what we do, is we, we put stuff in the
way of this electron on its path, and this is where
we build our circuits. So the, 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 gonna redraw
my circuit and my battery. I'm gonna flip the battery around it 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, this is the nomenclature for conventional current
or just plain current.