There’s been a lot of discussion recently on different models for teaching electric circuits. But there’s one really useful model that seems to have been overlooked in the discussion and might be new to some. So, here’s a reintroduction to the idea. I’ve illustrated all the main points below with animated gifs. Each animation has a link below it to an actual piece of software, so you can use it yourself right away in your browser. Everything is shared for free, runs on PC, Mac, Android and iOS and while I know IT doesn’t always get an easy ride in schools, it’s all programmed in HTML5 so it blinking-well should work.

I won’t rehash a discussion of other models since there’s a great overview by Tom Norris here. Tom argues well for his version of the rope model. And here’s an overview of the coulomb train model. These models are obviously very well thought out, but I would argue they both get a tad clumsy when they tackle parallel circuits, needing overlapping sections of rope or track before and after the circuit separates into branches.

So, with the preamble over, here goes, I’m going to say it: I think the big problem with circuits is *potential*. Most students will have come across and should be comfortable with the ideas of electrons and charge before they get to circuits. For current and resistance, the clue is in the name. We’ve all experienced things that flow such as rivers, traffic, or students along a corridor, so it’s not a huge leap to imagine current as electrons flowing and from there, resistance is anything that impedes the flow of those electrons. I’m not saying these concepts are easy, just relatively not as hard as potential. (BTW I’m using the word *potential *and not *voltage* throughout because for me it seems to communicate the ideas better).

Below is a model of the simplest of circuits. You can blend from a realist view, through a circuit diagram and onto an abstract view. The abstract view starts with arrows to show current, but you can then switch to a view of the electrons. The pink circles around the electrons show the relative potential of the circuit at different places. The higher the relative potential, the bigger the circles. In short,* the pink circles enable you and your students to visualise and discuss what happens to potential through a circuit.*

*This is looping an animated gif. Click here to try the real thing.*

All together, the pink circles show the extra energy given to the circuit by the cell. To put it more mathematically, E=QV so if you add up the potential of every charge you get the energy. And you can see this energy being dissipated through the bulb with emanating pink circles.

This model clearly shows students why a voltmeter has to go across a component: it measures the difference in the potential – the difference in the sizes of the pink circles – between two different places.

Here’s a series circuit. Use it to show how the potential drops across both resistors. You can then show how the drop in potential across one resistor increases as you increase its resistance.

*This is a looping animated gif. Click here to try the real thing*.

But the real strength of this model is how it helps with parallel circuits. In the below circuit, students can see the change in potential is the same through both branches of the circuit. If you decrease the resistance of one resistor, you can show how the potential difference across it is unchanged while the current increases. You can see P=VI now: power is the rate at which the electrons flow multiplied by the energy lost as it passes through the resistor.

*This is a looping animated gif. Click here to try the real thing*.

And the real *pièce de résistance* is how this model copes with AC circuits. You can start with a low frequency to show the current moving back and forth. At a higher frequency the bulb barely has time to dim.

*This is a looping animated gif. Click here to try the real thing*.

Another great advantage of this model is the minimal cognitive load as you morph from a picture of the circuit to the abstract view. Other models have big conceptual leaps like “imagine I am a battery”, or “the wire is like a train track”.

There are at least three problems to watch out for. The first is that because it looks a bit like how a real circuit works, students might think of this as a representation rather than a model. My answer to that is the reality of how circuits work is even weirder than most people think – look up Poynting vectors if you don’t already know – so every idea we’re trying to get into students’ heads at this stage is a long way from reality and we need to make this clear however we teach it.

The second problem is the potential misconception that the energy is given to the electrons rather than added to the electric field as a whole. I’d argue this is a slightly moot point since electrons are the only constituents of an electric field anyway. Even if students do get this misconception, it’s not the worst one to have by a long stretch!

Thirdly, there’s the problem of how few electrons are shown. If you’re worried about this, you might say the blue dots represent a coulomb’s worth of electrons. Then it’s more like the coulomb train model and the E=QV maths has simpler units.

So, advantages:

- Can “visualise” the trickiest concept of potential
- Clearly demonstrates current and resistance.
- Low cognitive load as the real circuit blends to the abstract
- Explains parallel circuits well
- Works for AC and DC
- Connects easily to the maths of E =QV and P=VI.

I hope the above gives you some useful stuff to use in lessons straight away. But because my children complain as much as anyone’s when we can’t feed them, if you want to make your own circuits, explore different components, create current/voltage graphs and much more, we have an App for sale for iPads and Android tablets from which all these examples were created. Stick your tablet on your visualiser and you’ll be able to build and explain circuits in front of your students for a tiny price*. And if you want your students to build circuits and practise those practicals before they get to the real stuff, it’s 50% for 15 or more copies in the App Store.

Thanks for reading, please add a comment, good or bad!

*If that price is too high for you, contact me on Twitter and I’ll send you a code to unlock the App for free (first 100 requests only!)