Electrical Circuit
Electricity and Magnetism

Physics and teaching models are different from analogies

Teaching Guidance for 11-14 Supporting Physics Teaching

Reflecting on teaching models

Thinking about the teaching

All teaching models and analogies have their strengths and weaknesses and it is important to be aware of what these are, and how they'll help or impede pupils as they try and come to terms with electric circuits. We don't think that all (teaching) models are of equal value to learners. We have advocated consistent use of a rope loop model, and given some of its advantages. You'll have to decide on one (and we think it should be one – or else the pupils need a very deep understanding of electrical loops to be able to select from amongst the models available to them, to apply the situation at hand), and we think you should be prepared to justify your choice.

We think it is not good to teach electric circuits as a collection of to-be-memorised rules, as this undermines pupils' confidence in their ability to make sense of the phenomena.

When using a teaching analogy in class, we find it very helpful to talk about it as a picture and to avoid calling it a model. This helps distinguish between helpful pictures (teaching analogies) and models: things you can reason with and that have predictive power. Both the electric circuit model (the scientific model the pupils are beginning to understand) and the rope model are worthy of that name.

We suggest you aspire to develop a model, with which the pupils can reason. Then use the model consistently. We don't recommend flipping around amongst models, because in such a case the short time that they have to study circuits will not be enough to acquire fluency with any one model. We certainly don't suggest that this is a good area for pupils to be asked to discriminate amongst models – there are far too many conceptual tripwires in this topic (and some models guide pupils into the trip zone).

One other common model involves energy being given to the charged particles as they leave the battery, which is in turn given to the bulbs. Energy may be modelled as loaves of bread given to breadvans (so the vans are the charged particles) or sweets given to pupils. All of these might be grouped as donation models.

A strength of the donation analogies is the way in which they distinguish between energy and current. The point was made earlier that pupils can easily mix up current and energy, so the teaching analogy directly addresses this problem.

However experience shows that this can also be achieved with the rope loop model.

A significant weakness of the donation analogies is that it paints the picture of charged particles collecting energy only in the battery and giving out energy in the bulb. As detailed earlier, this is not the case. The physical reasoning is wrong, even if the sums done later exhibit similar structure. The analogy does misrepresent the physics – think back to lessons of the big circuit, and is likely to reinforce many of the wrong tracks identified in this topic.

A further weakness of donation analogies is the reliance on ad-hoc rules. For example, using a supermarket picture, in moving from one to two bakeries, it may be plausible to suggest that each van collects twice the amount of energy, but it is not so clear as to why the vans also move round at twice the rate. For the correct working of the analogy it is essential to recognise that changes to the amount of bread carried per van and the rate at which the vans move round cannot occur independently. Similarly, in adding an extra supermarket it is necessary to accept that the bread is shared between the supermarkets and that the loop of vans is slowed down.

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