An Analogy for Resistance
One of the features which I love to include in teaching physics is analogies. These are so crucial, and there are so many out there, so picking the right one is key. The area where these are most commonly used is when teaching electricity. I was lucky enough to be taught by an amazing Physics teacher when at school, and I still use his analogy now, it is definitely my favourite of all time.
The analogy is for factors that affect resistance, and it fits so perfectly. Students always seem to remember it.
First of all, you need to set the scene:
Imagine in the corridor outside of your classroom, you probably have some lockers. Now think about this just at lesson changeover, or just before school. You will have a plethora of year sevens. They don’t know where they’re going, what they’re doing, who they are, and have probably lost the key for their lockers. They’re bumbling around aimlessly. This bit is good, as 99% of the time, it is true. These are our metal ions in a wire, gradually vibrating around the fixed point.
Now, you make it relevant to the students you’re teaching, anyone older than year seven:
Ask them what would happen when they walk through that corridor. At first, they say they’ll walk around the year sevens, but press them again, ask them to be honest. That honest answer which you’re looking for is that they’ll bump into the year sevens. These older pupils are the electrons in the circuit (size-wise I know there’s a problem, but lets run with it for the analogy).
You need to explain that every time they collide with a year seven it makes their journey harder, this is what increasing resistance in a circuit is like, making the movement of that electron more difficult.
So now we need to look at factors which affect resistance. There’s three which are discussed at GCSE:
What would happen if you made the corridor narrower? Would you collide with them more or less often? The answer is more – they now know that the thinner the wire the greater the resistance.
Secondly, we make the corridor double the length, the same amount of year seven again in both sections. What happens now? How often do they collide? Well, the answer is more, they collide more, so they’ve now learned that the longer the corridor the greater the resistance.
Finally, and this is my favourite and the one that they remember best! We blindfold the year sevens and we send someone out with a bunsen burner. What do the year sevens do? Students will talk about them running around, this is where you need to relate this to the vibrations of the metal ions. We tie it back to the analogy, how often would they collide? Again, the answer is more often. So they’ve now learned that the hotter the wire the higher the resistance.
So, within the space of around 5 minutes of teaching, you’ve gone from an abstract concept which students find hard to visualise to one that they’ll remember because of the way you’ve taught it!