Things are not going as planned. I’ve run from group to group checking that they’ve got the circuits set up properly. Most haven’t.
I stop the class and end the practical.
I’ve scanned the results and only two groups have any that vaguely resemble what I expected.
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“So, have a look at your results. We’ve connected two lamps in series and measured the current passing through them by putting ammeters in different positions. What are your results, and what do they tell you about current in a series circuit?”
Multiple hands go up. I deliberately pick one of the two groups that got half-decent results.
“Our first ammeter was 0.19, and our second ammeter was 0.17."
“Great, thanks Chris. What does that tell you about current in a series circuit?”
“It goes down”.
Not good. I can hear the misconceptions simultaneously clunking into place in 32 Year 7 brains.
“Thanks, Chris. Similar values, though, aren’t they? Jenna, what about your group?”
“We had 0.21 amps on the first one and 0.19 amps on the second one”.
“So what do your results show you, Jenna?”
“Same as Chris said, the current gets lower after the second bulb."
The bell rings, and I’m left wondering what just happened.
For a large portion of my career, teaching electricity has been a real challenge. I know I’m not alone; when I’m running physics teacher training, electricity is the first topic teachers want help with.
Why is it so hard? There are multiple reasons. For starters, it’s abstract; we can’t see what’s going on inside the wires, so we have to use (often flawed) models to describe what’s going on.
What’s more, the results we see in practical investigations often contradict what is predicted by theory. And the kit frequently doesn’t work.
So what can we do to overcome these challenges?
Electricity lessons: start with charge
Many secondary science schemes of work start with the practical side of electricity; building and testing circuits. This leads to pupils making observations as to how electric circuits behave without any actual understanding as to what’s going on, possibly leading to misconceptions that are hard to undo later on.
I’ve found it far more beneficial to start with the (albeit abstract) concept of charge and what’s happening inside the circuit.
Start with magnets; pupils are usually pretty good at remembering that opposite poles attract and like poles repel, and this primes them for understanding how charge behaves.
Then introduce models. Be explicit about the limitations and misconceptions with each as you go through them. The rope model is a great way of helping pupils to understand the relationship between current, potential difference and resistance.
I find a donation model, like the Coulomb Train Model (as described here by Gethyn Jones), is excellent for introducing the quantitative aspects of current and potential difference in series and parallel.
Plan effective practicals
I’ve already given a few tips on effective practical work here, and I can’t think of a topic where it’s more important than with electric circuits.
Take the Slow Practical approach the first few times and build it with them, step by step. A visualiser helps. When they start to get more confident, leave a correct circuit at the front of the lab for them to check their own against.
Do the practicals at the end of the topic (having taught the theory). The results rarely match the theory and can embed misconceptions.
Get shedloads of practice
I’ve already written about the benefits of SLOP in a previous article, and I’ve found it to be crucial for developing pupil confidence in dealing with electric circuits.
There are six electricity-specific formulae that pupils need to be able to recall and apply in the GCSE Science specification, plus rules for current and potential difference in series and parallel circuits. Pupils need to practice these until it becomes second nature.
Going goal-free with circuit diagrams is also really useful. When pupils are given a problem to solve they can become so caught up in trying to find the correct answer that they don’t have enough working memory left to remember the strategy they’ve used.
They might get the correct answer, but when faced with a similar question later they’ve not remembered how to solve it. Removing the goal reduces the cognitive load.
For example, rather than give pupils a circuit diagram with the question “find the current passing through lamp A” you could give the pupils a circuit diagram with some of the values labelled, and ask them to discuss what else they can deduce from the diagram.
Chances are they will find the value of the current in lamp A (and other values, too) but by reducing the focus on one particular answer, pupils are more likely to remember the strategies they’ve used.
Bob Pritchard is lead practitioner (physics) at St John Plessington Catholic College