This post will tackle the age-old question what is electric current?
It is another write up on a basic, yet fundamental and important topic.
We’ll also try to keep this one a bit shorter than usual. After all, I know the nice long holiday weekend is on everyone’s mind (at least if you live in the U.S.) and I’m no exception.
Plus, this fundamental question shouldn’t take 2000 words to answer.
As usual, I’ll give a similar disclaimer to the ones I often give for posts on the basics. Some of you already know this. If so, it will be a good review. If you’re just starting to learn about electronics, the information in the post is need to know, so please read it.
And now let’s find out the answer to what is electric current…
What is Electric Current?
Electric current, or just current for short, is the flow or movement of electrons.
Okay, so now you know the answer and we’re done. See you next time…
The above is definitely true, but let’s take a closer look at what this means, how it happens, and some terms associated with current flow.
Atomic Physics Crash Course
We know that current is the flow of electrons.
Anyone who’s a graduate of the 4th grade probably also knows that electrons are small particles inside of atoms. In case you forgot some of your 4th grade science lessons, figure 1 shows the basic structure of an atom.
Figure 1: basic structure of an atom.
The picture on the left of figure 1 is a 3D representation of an atom and the one on the right is a flattened 2D version for clarity.
There are a few things to note about the atom.
First, the electrons are very small and have very little mass. Also, the nucleus, which the electrons orbit around, is made of protons (which have a positive charge) and neutrons (no charge).
Finally, though the picture depicts the nucleus of the atom as being large, it is indeed actually quite small in comparison to the size of the whole atom. So small in fact, that if the atom was drawn to scale, you wouldn’t be able to see the nucleus in the figure 1 at all. But, for the purpose of demonstration we’re going with figure 1.
In order for electric current to flow, electrons must jump from atom to atom.
Conductors are materials that give up electrons easily – things like copper, gold, aluminum, silver and most metals.
Insulators do not give up their electrons so easily. These are things like glass, porcelain, wood etc. They inhibit or prevent current flow.
Electric Current and Counting Coulombs
Now that we got basic atomic structure out of the way, let’s talk about a unit some of you may not be familiar with.
The unit of measurement for electric current is the Ampere or Amp for short. The symbol for the Amp is the letter A.
Okay, most of us know this but what exactly are amps? Are they just electrons, or is there more to it?
Turns out there’s more to it.
Electrons have a negative charge.
Coulombs are the unit of measure for charge (charge has the symbol Q).
One Coulomb is equal to the charge transferred in 1 second by 1 Amp of current. Put another way, 1 A = 1 Coulomb per 1 second.
This simplifies to A (current) = Q (charge) divided by t (time in seconds).
Therefore, current is equal to the amount of charge transferred per second. One Coulomb of charge contains 6.24 x 1018 electrons. So, 1 Amp is 6.24 x 1018 electrons moving past a given point in a circuit in 1 second. That’s a lot of electrons!
To shed some clarification on this, have a peek at figure 2.
Figure 2: definition of the Ampere or Amp.
The red vertical line in figure 2 is some arbitrary point in the circuit; it does not matter where we put it. In order for us to have 1 A flow through this simple circuit, we need 6.24 x 1018 electrons to flow past this point in 1 second.
Here’s an example problem to drive the point home.
Suppose 5 x 1019 electrons pass a point in a conductor in 2 seconds. How much current is that?
To figure this out, we first need to see how many Coulombs 5 x 1019 electrons is:
(5 x 1019) / (6.24 x 1018) = 8 Coulombs.
Then, we divide the number of Coulombs by the time in seconds:
Q/s = 8/2 = 4 A.
From a practical standpoint, you likely won’t be counting electrons at your bench or measuring Coulombs, so let’s back away a bit and take a quick, higher-level look to answer the question what is electric current.
What is Electric Current?: A Simpler Abstraction
A while ago I wrote a similar post about voltage called Back to the Basics: What is Voltage?
In the post is a simple analogy to help electric newbies grasp the concept of voltage. Here, I’m going to use the picture and analogy again.
Figure 3: water voltage analogy.
To quickly recap, we can think of the pump as the battery in the circuit from figure 2, as it causes something to move (the pump moves water, the battery moves electrons).
The valve is like a variable resistor. When it’s all the way closed, no water flows. When open all the way, maximum water will flow.
Finally, the water flowing through the pipe is like the current flowing through the circuit. Just as the current in the electrical circuit does work by lighting an LED or spinning a motor, the water can do work if, say, we set up a water wheel at the end of the faucet.
So, if 6.24 x 1018 water molecules flow past some point along the pipe in 1 second, we have 1 Amp of water flowing.
Well — not really, Amps deal with electrons not water.
Anyway, just like excessive water flow in figure 3 can burst the pipes and be dangerous, excessive current flow can also be dangerous. If too much current flows in a given circuit, it creates heat which can burn up wires and components and cause a fire. So be careful when designing your circuits and make sure your components and wires can handle the electric current you expect to flow. Also, be sure to include a fuse in your projects. A fuse will open, breaking the circuit in the event too much current flows. This can prevent fires.
What is Electric Current? A Quick Recap
Let’s end this short post by doing a quick review.
Current is the flow of electrons and is measured in Amps. An Amp is a huge number of electrons flowing past a certain point in a certain amount of time. Unless we work in some research lab though, we likely won’t be counting electrons.
What’s important for most hobbyists is understanding that current is just moving electrons, like the water moving through the pipe in figure 3. Also, knowing how to calculate it using Ohm’s Law is important.
We didn’t talk about it here, but for more on Ohm’s Law and calculating current see Simple Circuit Analysis Techniques You Should Know.
And that’s all we need to know about electric current for now. I hope I’ve answered the question what is electric current?
Until next time, drop a comment and tell me what topics you’d like to know more about. These can range from the basics like this post, to more complicated stuff. Let me know how I can help you!