The approach to teaching energy has been a hot topic in physics for a while now. The long-established approach has been to list different types of energy and then to think of physical processes as involving transformation of energy from one form to another. Although it’s not inherent to this way of thinking, it’s quite common for physical processes to be explained in terms of these energy changes too.
For some time now, the IoP and others have been strongly promoting an alternative approach which sets clear start and end points and considers different types of stores of energy, with conservation of energy dictating that as one store empties, another fills. Linked to this alternative approach is a clear emphasis on energy as a calculation tool only and not as a way of explaining processes.
Now that the new KS3 NC and the new GCSE Subject Content have both been written in a way that favours this new approach to energy, it is clearly necessary for me to ensure I am not only passing this approach to teaching energy on to my trainee teachers, but also exploring the ramifications for other bits of science teaching. This is something I’m struggling with quite a bit and I ran into a significant issue earlier this week in tweaking my session on basic circuits.
My approach to basic circuits is to start with potential difference and sort that out before dealing with current. The thinking here is that p.d. is the most conceptually difficult part of circuits work and the usual problem is that p.d. and current are not well enough separated mentally, so misconceptions like p.d. splitting when components are in parallel are common. By teaching p.d. first, that can be secured before grappling with current; doing it the other way round means that p.d. is being taught whilst students are in the process of grappling with current and so inevitably the two get conflated. Regardless of the merits in this order of teaching, a clear concept of p.d. is necessary, and I’ve always approached this by invoking energy.
If p.d. is a measure of the change in energy between two points (change in energy per unit charge, obviously, but I would tend to avoid that technical detail at first) then it becomes fairly easy to be convinced that the change in energy across the power supply must equal the change in energy across the other components in the circuit. Equally, it makes the idea of p.d. splitting across components in series but not across components in parallel fairly clear too. This is really all based on the idea of conservation of energy but I find kids get that pretty instinctively. Anyway, I’ve been teaching it this way for a long time and with a pretty high level of success as far as I can tell (albeit generally with fairly high-achieving students).
But you can see the problem – talking about energy like this is not going to sit comfortably with the new approach to energy at KS3/4 because in that approach, the circuit system would be described as a chemical store of energy in the cell being emptied, and a thermal store of energy (in and around the other components) being filled. There is an electrical pathway transferring energy from one store to the other but talking about amounts of (electrical) energy changing around the circuit doesn’t fit. I did try it this way with my trainee teachers this week; I related p.d. to the rate of emptying of the chemical store, and the rate of transfer to the thermal store. It kind of worked but did feel a bit clunky.
So possibly it’s just a case of everyone getting up to speed with the new approach, and then it won’t feel clunky. Another possibility is to teach the energy topic using the new approach and then not get too hung up on it within other topics (like how at A-Level we happily ignore quantum models when teaching interference of e-m waves) but that seems like an unhelpful compromise as far as childrens’ understanding is concerned. Is there an alternative?
A quick Tweet for suggestions, and a brief flurry of ideas, and the one that caught my eye was this:
Could this be an alternative approach to p.d. that allows teaching it first in a way that establishes a solid foundation for subsequent work? Maybe.
Here are the diagrams I use for establishing what a potential difference is.
At the moment I talk about the movement of electrons creating a ‘difference’ between ends of the cell, or parts of the circuit. I then name this ‘difference‘ a “potential difference“. An alternative approach is to emphasise that the charge has to be evenly distributed along a wire and name this as all points on a wire being at the same potential. It then becomes fairly clear that the difference across components is a potential difference. If you focus on the underlined words then there has been a shift from talking about differences to talking about potentials. Maybe this slippery technical term means the alternative approach is going to be a harder sell but on the other hand it does offer a way to avoid energy altogether. Does this advantage outweigh that problem?
I would be really interested in anyone’s thoughts.