Electricity teaching order
Establish a mental model early on
A common approach to teaching electricity is to let students set up circuits straight away to get some hands-on experience.
The trouble with this approach is that students will very quickly start building sub-conscious mental models of what's happening, which will tend to be the ones that stick, rather than anything they might be explicitly taught.
So we want to start with a story about why electricity's useful and a simple story about what happens inside circuits before we try to get students building circuits.
Tell a separate story about electrons in wires
The idea of conventional current causes confusion amongst students and a great deal of irritation for many teachers.
One way of getting round this is to be bit sneaky and deliberately not connect our story about charges and energy with our story about electrons. For example you could talk about electrons in a generic piece of wire, rather than all the way round a specific circuit.
Any student who spots that there is an inconsistency is probably ready to understand the need for conventional current.
Voltage and current are handled individually before they're linked
Many courses are obsessed with Ohm's law and rush into the relationship between voltage and current.
Our story is about how charges transfer energy around a circuit. We want to be able to explain what's happening in circuits where voltage isn't changed before we start worrying about the concept of resistance.
Power: joining voltage and current
We want to describe why bulbs are bright or dim and how long it takes for batteries to run down. This involves the idea of power.
A bulb is bright if charges with energy arrive at a high rate and transfer lots of energy before they leave. This is why power depends on both current and voltage.
Electric devices are designed to work at a certain operating voltage and to begin with we don't try and run them at anything other than this.
Resistance: running devices outside their operating voltage
At this point we bring up the ideas that big voltages cause big currents and that big resistances cause small currents for a given voltage.
We also want to account for why energy is transferred where the resistance is biggest but that the bigger the resistance the slower energy is transferred.
All of these concepts are quite difficult to grasp and we hope that by delaying them until now students will have a solid enough grasp of the basics of charge, energy, current and voltage that they can cope with a little uncertainty.
Parallel circuits are normally taught after series circuits. They tend to look more complicated and the formula for effective resistance of a parallel circuit is more difficult to use.
However parallel circuits are more useful and more widespread around the home and they link in nicely with the idea that the more appliances you run the quicker energy has to be supplied.
We leave these to the end because they are much more difficult to understand properly.
In particular there is a temptation to explain why two bulbs in series are dim in terms of current only. This leads to the incorrect assumption that two bulbs in series are roughly half as bright as one bulb alone whereas they are really about a quarter as bright.