The deserts of Afghanistan inspired Lewis to become a physics teacher. Now he is a Head of Physics. In his first placement, eager to put theory from his PGCE into practice, he prepared a lesson on Faraday’s and Lenz’s laws …
I made up my mind to start teaching while in Afghanistan where I saw first-hand the importance of education – or lack of it. A year later, I really enjoyed being back at university studying for my PGCE and I couldn’t wait to get into the classroom to put into practice the theory we had covered in the lecture halls.
At my first placement school, I was allowed to teach small lesson segments to a Year 13 physics class of about six high ability pupils. They had been covering electromagnetism and were about to study Faraday’s and Lenz’s laws. I planned the lesson with the idea that I could show them a demonstration, explain the concept and then they would understand it. This was a rather naïve view that has since changed.
This was the plan…
The demonstration was fairly standard. I had spent time talking to the very helpful science technicians as we trialled various magnets and coils. I would drop a small bar magnet through a coil that was set up to a data-logger that could record the potential difference across the terminals of a long cylindrical coil.
As the magnet dropped, it would cut through the magnetic flux lines causing an induced electromotive force. If this was recorded, the graph should show how the voltage changed with time, with both positive and negative values. The second peak would be larger than the first since the rate of change of flux should also increase as the magnet accelerated.
Here’s how it went…
As the class waited for me to begin, I felt my physics knowledge was good, I had a demonstration which would wow them, I understood what was happening, I had read around the topic in the textbook: what could go wrong?
Well, firstly, the data-logger was not registered by the computer in the classroom, even though it had worked fine with the laptop I had trialled earlier. Fortunately, it finally warmed up and the eager students crowded round.
I explained what I was about to do and the result we should expect. The graph, although small, was correct and by changing the direction I dropped the magnet, it flipped as I told them it should.
So, I had shown them an experiment and explained what was happening, backed up with plenty of PowerPoint slides to reinforce what I had just told them. I felt I had ‘taught’ the class some new knowledge.
But had it been a success?
Later in that first lesson, I set the class some questions to work through to find out whether they understood the concepts I had lectured them on and if they could apply that knowledge in a new situation.
These proved to be harder than I imagined. I had to constantly move from group to group answering the same queries. I was disappointed to find that the students were struggling to get started and didn’t see how what I had just taught them could be used in that context.
I discovered that although I had told them about one particular aspect of Faraday’s Law, in fact they did not understand the basic principles behind electromagnetic induction. It dawned on me that telling them information did not mean they had learnt the physics behind it. Lecturing facts did not necessarily cause learning.
How I teach this topic now
When I teach this topic now, I get the students to investigate the effect of the number of turns, the direction of the magnet and the speed of their relative motion by reading on a galvanometer as they use various magnets and coils.
We then come together to see a similar demo to the one I showed in my first lesson. But we discuss what result they should see – if you tell them what to expect then why use the demo at all? Their discussions, led by prompting questions, allow them to formulate their own ideas which will deepen their understanding. Telling them facts will not achieve this.
Their discussions develop during the lesson as they explain their ideas to each other and this allows me to guide them and address misconceptions. I try to find problems which challenge them to apply their new knowledge to new situations – for example, generators and graphs of the output potential difference that they construct, not just copying the correct answer from the board.
What I learnt…
Demonstrations do work and add interest, but the students need to have as much hands-on experience as possible and discover for themselves. Practical work makes our subject come alive and shows we are not theoretical maths teachers.
Plus, I found out the hard way that you have to test your experiments and demonstrations in the classroom you will use, check the ICT works and become self-reliant in the set-up of the equipment: your technicians will be excellent but if it goes wrong you are the one the students look to.
As you spend time planning lessons, you must put yourself in your students’ shoes. What do they currently know? What would be interesting? How could they demonstrate their new understanding to you? This is not an easy task and certainly not one that experienced teachers always get right. As you teach more, you will remember what works for each topic, which demos and practical tasks help their learning and how they can take an active role in their own learning.
Links to related resources
Practical Physics: Electromagnetic Induction (IOP/Nuffield Foundation)