10. Ways to teach… Electricity

Merry Christmas Physics teachers!  In a bumper festive edition, Thomas and Robin have rounded up your ideas and tips on how to teach electricity.  It’s quite rare to reach a clear conclusion in a discussion of teaching, but there was consensus that if you are going to use a model, then the rope model is a great starting point, and Thomas has written a full description of a way to use the rope model in his blog.  We also acknowledged some other models and their usefulness: the important thing is to reflect and evaluate, but then again isn’t it always?


You can see all the tips and suggestions in a gallery at the bottom of the page.

We were delighted that the excellent PhET resources were mentioned by a couple of people. There are several electricity simulations, for example the DC construction kit.

Robin mentioned the Supporting Physics Teaching Web site, and its resources on electricity. It’s a great resource but is more akin to an Encyclopedia than a guide.   For a nice clear description of the rope model read the article by Tom Norris about teaching electricity. Tom also sent us a message after the interview:

Traditionally, in ks3 electricity schemes, you teach the electricity concepts, and *then* comes a lesson where you teach about electricity models. I personally wouldn’t do the “evaluating models” lesson unless I’m happy students’ understanding of electricity itself is at an expert enough level to be able to spot the subtle nuances of what the models do well and not so well. And also, secondly, because I don’t think knowledge of electricity models is anywhere near important enough to give a whole lesson to. The most important resource physics teachers have is time, and I the electricity topic I want to spend every lesson teaching about electricity itself. I don’t see electricity models as ‘content for students to learn’, rather, electricity models are something that I, the teacher, turn to, to help me explain/demonstrate the electricity concepts that I’m teaching.

Tom Norris

Lucky shot of an arc sparking

Thomas was delighted by the idea of driving a aluminium foil capacitor with the EHT. He duly did it and was delighted with the results.

What an exceptional community we are building!  All of this week’s podcast came from our growing listenership, so a million thanks.  Keep spreading the word, and if you liked the slightly different format (or not!), do let us know.  Similarly, if there’s anything you’d like to cover, please do share.  We plan another special on energy soon.

Have a good rest and we’ll see you in the New Year!

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Using The Rope Model of Electricity

In the next podcast we inevitably talk about the rope model. I tried it a few times in the past and hated it ūüėĚ. It was only in making the podcast that I finally understood how to do it and how good it is. Not knowing how to do it is as much a function of my comfort with the donation model as it is my being alone in my school with no other physicist to talk to. But talking to Robin and Stuart about electricity really got me thinking. 

When I did the rope model it didn’t work because I had quite a few kids involved in the demo. I found it really hard to make the rope run smoothly through their hands (not least because the rope had a huge knot in it!) and it was a very static sort of demo. There was no fluidity at all, no flow. I had visions of attaching pulleys to the walls of the room to make it work (I like big scale). I chatted to Stuart about this and he was able to tell me a way to do it that worked. It works so well, and is so easy to do. I was bowled over.

my recipe for an effective rope model demo:

  1. Have a rope that is in a 3-4m loop where the join is as smooth as possible. (Cutting and melting together a rope is ideal).
  2. Choose one student only.
  3. Hold the loop and pass the other end to the student. Tell them to grip it lightly (they don’t want rope burns) in one hand with the rope passing vertically down through their fist¬†(this is the detail I never understood – one student, one hand).
  4. Explain that the rope is the electrons and the grip is the resistance.
  5. Pull the rope hand over hand through their (one, stationary) hand.
    • Question: What do you feel in your hand?¬†
    • Answer you want: Warmer
  6. Tell them to add another hand, holding with the same light grip. The rope will get harder to pull, make this obvious, it will naturally run more slowly.
    • Question: why is the rope moving more slowly?
    • Answer you want: because there is more resistance.
    • Question: how can I increase the current to make it move as fast as before?
    • Answer¬†you want: Pull harder.
    • Explain that this means more energy being delivered by the cell to the rope, or greater pd.
  7. Pull harder, to make the rope move at the original speed again.
  8. Tell them to grip tighter with one hand, but not to tell you which hand that is.
    1. Question: what has happened to the rope speed?
    2. Answer you want: slower.
    3. Question: does the rope/the pd know which hand is gripping harder?
    4. Answer you want: no.
    5. Question: what is happening at the tighter hand?
    6. Answer you want: warmer.
    7. Explain how this is energy transfer
    8. Question: are the electrons in any way different before and after the hands?
    9. Answer you want: no.
    10. Remind them that electrons just go where they are pushed/pulled by the pd, they aren’t changed, they don’t make a choice, they just go where they go.
  9. Get another rope, get them to hold one loop in each hand, but you pull them together. You can model parallel with this but I wouldn’t go too far as the model does tend to break down a bit.
  10. You can show AC nicely too. Remove one loop then tell them to hold their fist horizontally, not vertically. Now grip the loop in both your hands and pull it backwards and forwards. The hand gets warm just the same.

Good luck with this. Maybe report back in the forum?

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Somebody Out There Likes Us

Robin and I started with very limited ambitions, it wasn’t quite “more listeners than presenters” but not far off. We agreed to do episodes until the end of the academic year and then see where we stood. At that point we had not got much further than me telling Robin he and I should start a podcast and then months later him finding the statistic that about 50% of schools in the UK have one or zero physics teachers. We just wanted to try something, try to build a community and see what happened. I am a regular listener of The Cycling Podcast and modelled a lot of our approach on them.

As we started I had no idea about format, content, approach, social media, iTunes ratings, post production, how to talk to a microphone and had never considered a T-shirt or shop (or adding a forum) But I am top loaded with running web sites and general geekery, so I figured I would muddle through.

It was a revelation to me (physics teacher, but never an audiophile) to find that a microphone has preferred orientation. Listening back you can tell the episode where I worked out where to point my mouth when recording.¬† I found a great T-shirt supplier when looking for somewhere to buy a jokey shirt for Robin. They actually make the shirts on demand and provide a WordPress plugin, so one thing led to another and now… a shop! Just a bit of fun of course, as Robin says in Episode 9, this is nothing about money… But if it helps build a community then that’s brilliant.

As I went to sleep on the night before episode 1 I was not convinced I wouldn’t grab my phone at 4am and cancel it. Now, as we approach the recording of episode 10 I feel more comfortable hearing my own voice. I’ve also been dragged kicking and screaming in to social media and I feel a community is growing. (We have had a few emails thanking us for doing it and the interaction on Twitter has been fun). It has also been hugely enjoyable talking to different people and learning from them: I recorded another PIM this week which will most likely be in Episode 11. Please do continue to send us ideas. We love hearing them all. You can use the form below.

Finally, to get some 5* ratings in iTunes is pretty stunning to be honest, so thank you very much, listener(s!).

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9. Mentors, Motors and Merch

Robin hadn’t heard about the recent Falcon landing failure so Thomas filled him in.  Cutting-edge space technology is still frontier science: we need your students to be the engineers of tomorrow!  Regular listeners will know how much Matt Groening influences the podcast, and just in time fro Christmas, we have launched our first ‘merch’, setting up a shop on the web site.  A shop where you can buy the T-Shirt? Yes, all your Christmas present problems are solved!  Listen out for a secret (??) code that allows you to get your shirt at cost. This time next year we may be stocking TPTP box sets and underpants: our ambition knows no limits.

Care in the community…

Physics teachers can be empathetic too! Robin worries about how hard this time of year can be, and especially for young-in-service teachers and the terrific Jo Kent draws on her wealth of experience to give her advice. She highlights how an empathetic ear can make all the difference, and on a more practical note, how networking can help to build communities.  She specifically mentions TalkPhysics and Thomas compares it to PTNC. (The IoP has a page where several other ways of networking are listed). Jo goes on to tell us about her Pint Pot Motors in a Practical In Memoriam. Below you can see the images she talks about below and she also sent us her PowerPoint and the video her father made.

It remains a privilege and a joy making this podcast for you.  We love hearing from you and you are a very big part of the adventure; guide us, tell us what you want to hear about. It really is your podcast, so please get in touch: teachers of physics are our very favourite superheroes! 

Exciting news!  We have a forum now if you want to talk about the episode, Jo’s motor or anything else in Physics Teaching. 

Please share ideas or successes on our Facebook Page ‚Äď https://fb.me/physicstp .  You can also message us via our website contact form at the.physicsteachingpodcast.com, Twitter @physicstp, email using  the address given in the podcast (if we remember) or by leaving a voice memo using WhatsApp or Telegram to the phone number in our Twitter profile, +44 7898 814716 (don‚Äôt call the number, nobody will answer, just hold down the microphone icon and speak your message). Don‚Äôt forget to tell us your name because we may use your audio in a future episode.

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The music we use remains One legged equilibrist polka by Circus Homunculus.

Jo’s Pictorial Instructions

A Working Motor

The Motor Jo’s Dad made:

Also Thomas made the motor and shared it on Twitter:

8. Venn Hats, Meows and a Mysterious Tube

Mr Benjie

As David Bowie once mused “Is there seismic activity on Mars?” ( I think that’s what he said…), and who are we to argue?  So we kicked off discussing NASA Mars Insight Lander and then Robin confessed to group about his tendency to get on a self-righteous soapbox (see episode 7!).  Luckily this week’s chat was the perfect antidote to stress as he chatted to Carole Kenrick: primary teacher, secondary teacher,  artist and PhD student, she wears many metaphorical hats … and has a podcasting cat called Mr Benjie.

Carole tells us about two of the practicals she likes the most: decay-dice and mystery tubes. Decay dice take the simplicity of rolling one die, developing it in to a beautiful mathematical model. She uses mystery tubes from the Berkley Understanding Science web site and they kindly provide instructions to make them. Thomas couldn’t resist making a mystery tube of his own and “Thomas from the future” appears to tell how he got on.

Thomas' early prototype
Thomas’ early prototype

Carole also introduces us to “Physics Fairy” (no, really, check it out!) and explained how it came into non-existence from working with Force Goggles from the Supporting Physics Teaching web site.

New Competition – Closes 13th December

Help us with our planned “Electricity” episode by giving us your top tips… and pitfalls. Either tweet us with the hash tag #physicstpelectricity or comment in the thread on our Facebook page. Thomas and Robin will choose a winner on the 13th of December and will send you a signed copy of Ben Rogers’ wonderful book The Big Ideas in Physics and How to Teach Them.

It remains an enthralling and educational adventure making this podcast for you.  We love hearing from you and you are a very big part of the adventure; guide us, tell us what you want to hear about. It really is your podcast, so please get in touch: teachers of physics are our very favourite superheroes!

The music we use remains One legged equilibrist polka by Circus Homunculus.

Refutation Text for the Jelly Chair

I said in Episode 6 I would share what I came up with for the Jelly Chair lesson and refutation texts. I did put some thought in to this but think that there is room for improvement. I ended up writing a few sentences for the kids to do:

  • The ancient Greeks thought that arrows were pushed through the air by the god Apollo. We know this is wrong because‚Ķ
  • Many people think that objects will slow down and come to rest if no resultant force acts upon them but really‚Ķ
  • A typical GCSE level understanding of balanced forces allows a person to sit on a chair made of jelly. This is false because‚Ķ
  • Galileo showed that two balls of different weights accelerate at the same rate when dropped.. Before this people thought heavier objects fell faster but this is wrong because‚Ķ
  • Some people think the International Space Station has no forces acting upon it because it is in Space, the evidence that they are wrong is‚Ķ
  • When a helicopter is hovering it is very common for people to think that the weight of the helicopter has an equal and opposite force that is the down-force from the rotors. This is wrong because‚Ķ

I was particularly happy with the last one (though I have no idea if that is an actual misconception or not), and even happier when one of the students said something like:

The down-force is equal to the weight!

They had truly understood the situation, and was able to explain to their partner that the weight and down-force must be equal in magnitude and in the same direction as weight if the helicopter is hovering (not equal and opposite).

As I roamed the class and spoke to the students I was pretty confident the refutation sentences were having impact. The challenge is to use them again and again and embed them in my practice.

The podcast strikes again. Thank you Ben Rogers!

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