Why does the circuits work with conventional current? [closed]

Question

I have been reading a number of articles about current. They seem to suggest that "conventional current" flows from the positive terminal to the negative terminal but actual current flows from the negative terminal to the positive terminal.

Since the direction of current merely seems to be a matter of convention and can be interpreted either way, I am confused as to why an LED would not light up when a current is run through it in a "certain direction".

This has confused me, thanks in advance.

So the semi-conductors are designed upside down?

Answer 1

It all started when electricity was discovered. They knew about magnetic effects of current, so knew it had direction. But they didn't know what it was. So what do you do with imperfect information? Farady et al made a choice, tossed a coin as it were, that current flowed from the positive terminal of a battery (the zinc plate) and flowed to the negative terminal (the copper plate). This is called 'conventional current', to emphasise that it was indeed a convention. As long as everybody agrees what direction it has, and what it means, then everybody's diodes will conduct and block properly. As a convention, it's rather like do we drive on the left or the right side of the road? It doesn't matter, as long as everybody agrees to do the same thing.

Many decades after electricity was discovered, the role of electrons in its flow in copper wires and cathode rays was shown. Some people got upset that because their charge was negative, they were 'flowing the wrong way!'

So should we change everything so that current flows the other way?

Many reasons why not. Can you imagine how many meters and batteries would need their markings changing, text books re-writing, people re-educating.

In semiconductor devices, the P doped regions conduct because of the movement of holes, not electrons. These are positively charged, and flow with the conventional current. You may object that a hole is the absence of an electron, and at one level of mathematical truth you would be right. At another level, a hole is a fully paid-up card-carrying quantum mechanical particle like an electron. So in copper and N doped semiconductors, it's electrons that carry the flow, in P doped it's holes. Electrons only have a majority now, it's not unanimous.

A materials scientist working to develop new semiconductors has much more to worry about than does the electron or hole have the + sign. And for the rest of us, who just use the devices, it doesn't make the slightest bit of difference.

Going back to the driving convention, the left/right issue is far more worth fixing. The world is not unanimous on which side to use. Why do we tell time in base 12 and base 60? Should that convention be changed to base 10 throughout? There's far too much investment in either of those to change because it seems a cleaner idea.

There will never be enough impetus to switch the sense of conventional current. Electrical engineering has plenty of minus signs crop up when you do sums, eliminating one is not going to simply things overnight.

Answer 2

I think your confusion stems from an unclear understanding of what current is exactly. I'm going to assume that the part about the LED is just an example and that PN junction theory is outside the scope of this question.

Current is the rate at which charge flows in a circuit. As a consequence, positive current is in the direction of positive charge flow. For a long time, physicists believed that it was in fact positive charges that moved in a circuit (or at least they used it as a matter of convention). Later experiments revealed that in fact current is made up of negative charges flowing.

This is where I believe your confusion comes in. The thing is, current is not merely the direction of motion of a charged particle. The sign of the charge is equally important. A negative charge constitutes a negative current.

So when we say conventional current flows from positive to negative but electron flow is in the opposite direction, both terms refer to the same quantity. The negative charges flowing in a certain direction constitute a current in the opposite direction. So in that sense, there is only one "current", the flow of electrons is a microscopic view that is ignored when analysing circuits for simplicity.