What is Current

What is current

Like a breath of fresh air

Take another breath. When you breathe in you create a lower air pressure in your lungs than the air pressure around you. The higher pressure outside your lungs forces air to flow through your windpipe into your lungs. This is just like the flow of electricity. If you have a higher voltage on one side of a conductor and a lower voltage on the other, electricity will flow from the higher voltage to the lower voltage. Air current is the flow of air molecules from a higher pressure to a lower pressure. Electrical current is the flow of electrons from a higher voltage to a lower voltage. All you need is a conductor for the electrons to flow through.

Conventional flow and electron flow

Long before the electron was discovered it was already known that electricity acts as a fluid and that it can be made to flow from a high electrical pressure to a low electrical pressure. However, it was impossible to tell which voltage was the high pressure and which was the low pressure, or which way the electricity actually flowed. Everything known about electricity was inferred by observation of how electrical charges act.  However, if you see a lightning strike, you can see the electricity move from the cloud to the ground, right? The cloud must have the higher pressure and the ground must have the lower pressure. All you have to do is grab a sample of cloud electricity. Once you have the sample, you can compare it to ground electricity and see which is which. This is precisely what Dalibard and Franklin did in 1752 (see A Brief History of the Discovery of Electricity). After sampling electricity from a cloud, which turned out to be vitreous, they knew that vitreous electricity was the higher pressure and resinous electricity was the lower pressure. Franklin renamed vitreous electricity as positive and resinous electricity as negative. Electrical fluid flowed from positive to negative.

Oops, wrong way

By the time Joseph Thomson came along scientists had already figured out, due to certain chemical reactions that electricity was made of tiny particles. Some people already called them electrons. They also knew that electrons flowed from positive to negative thanks to Franklin and Dalibard. Then, along comes Thomson with his Crookes tubes and Maltese crosses and calls the cops on the party. He showed that electrons actually flow from negative to positive. The flow from cloud to ground during a lightning strike is an illusion.[1]

Another look at Thompson's Crookes tubes.i The shadow of the Maltese cross shows that particles are shooting from left to right.
Another look at Thompson's Crookes tubes. The shadow of the Maltese cross shows that particles are shooting from left to right.

Now what? Either announce that negative is the new positive, say “remember how electricity flows from positive to negative? Forget it, electricity now flows from negative to positive” or close your eyes, plug your ears, say “la-la-la-la” really loudly, and insist that “electricity still flows from positive to negative.” People who work on the technical level typically choose to say electricity flows from negative to positive. This is the electron flow camp. However, academia and the industry as a whole chose to pretend that electricity still flows from positive to negative. This is the conventional flow camp.

For the most part, it doesn’t matter one iota whether you imagine electrical current going from negative to positive or positive to negative. The circuits work the same either way you look at it. The only time it becomes important to follow the electrons is when analyzing certain components like vacuum tubes. University level educators and the electronics industry have chosen to use conventional flow to analyze circuits. Using this model, positive is greater than negative just as in other situations. Electricity then flows from a greater pressure to a lesser pressure, which is a lot more intuitive than imagining electrons flowing from a more negative potential to a less negative potential. Diagrams in data sheets for electrical components and circuits show conventional flow. The symbols for semiconductor devices (diodes and transistors) have arrows that point in the direction of conventional flow. Regardless of the model used by electricians and many technicians, the electronics world mostly revolves around conventional flow.

Imagining things acting backward from reality, because it’s more intuitive, is nothing new. You see the sun, moon and stars revolve around the earth every day. You know that it is indeed the earth rotating in the opposite direction, but when you watch a sunrise, you don’t say “my, what a beautiful earth rotation we’re having this morning.” With electricity, you can’t tell which way the electrons are flowing. It’s easier to imagine a fluid flowing from a high pressure to a low pressure than from a low pressure to a high pressure. You don’t have to explain it as electrons flowing from a more negative potential to a less negative potential or however you justify it. That’s why most of the industry uses conventional flow. Again, there are a few examples where you need to follow the electrons. However, for the most part, it is just a lot easier to use conventional flow to analyze electric circuits.

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1Electrons occasionally flow from cloud to ground during a lightning strike, but it's usually the other way around.