Direction of flow through a circuit
Did you know electrical current flows from negative to positive through a circuit? Many of you probably do, and it may not seem important, but the more you know about any aspect of what happens in electrical circuits, diagnosis of them becomes a lot easier.
To see this in action, I have created an animated gif file that shows electron flow through a copper conductor.
Conventional theory states that electrical current flows from a positive point to a less positive point. (arrows) Electron theory states that current flows from negative to positive and is based on the flow of electrons. (negative electrons)
In the animation, negatively charged electrons (right) are attracted to positively charged protons. (left) When a electron is pulled from the valence ring of a copper atom, Atomic Science Class the atom becomes positively charged (ion) and will attract an electron from the valence ring of another atom. This starts a chain reaction as one atom captures an electron that's released from another. As this continues, electrons will flow through the conductor.
You've seen this when you take current measurements on a circuit either with a DMM inline, or a DSO inductively. When you hookup to the circuit, you see either a negative amount, or a positive amount. Reversing the leads to your DMM, or inverting your probe will correct this and show you the direction of flow through the circuit. Some inductive probes will have markings to indicate the proper hookup to the wire with a negative symbol (-) and a positive symbol (+) on either side of the jaws of the probe. Try your probe on the output wire of an Alternator, which way is current flowing based on your probe markings? With positive towards the Alternator, it should be showing a flow into the Alternator.