## Standing waves on a spring

Posted: October 29, 2014 in Institute of Physics
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You might have seen/done this one before, but the teachers I was showing it to found it quite useful, so I thought I would post it on talkphysics. The nodes and anti-nodes are a lot clearer when the amplitude of the oscialltions is higher, but I was told the signal generator broke the previous vibrator when set too high, so I was a bit cautious with this one.

There are several teaching and learning points with this demo. For example, you could get the students to calculate the speed of the wave along the spring, as we know the frequency from the signal generator and can measure the wavelength (for example by measuring the length of the stretched spring with a ruler).

Once we know the speed of the wave, we could ask the students to predict the next frequency in which a standing wave will form.

What else would you use this demonstration for? What other questions would/could you ask?

## Phases of the Moon (with an infrared twist)

Posted: May 24, 2014 in Institute of Physics, Thoughts and ideas
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I recently was asked about the phases of the Moon and why the Moon appears to change in shape in its orbit around the earth. So I thought a good point to start from was to establish what misconceptions people have on this topic and I found this great video by Veritasium (but I would stop it at the end of the interview without revealing the explanation initially).

The most common misconception in the video seems to be that the earth blocks the sunlight reaching the Moon, hence, we see the phases of the Moon when it is behind the earth with respect to the sun. At this point I would slide two circles of card, a white and a black one (with the black one bigger than the white one) past each other (black on top). If the black card is the shadow cast on the Moon by the earth (essentially what happens in a lunar eclipse), the shapes of the Moon due to the light reflected back to earth are considerably different than the shapes we observe from the phases of the Moon. So, we have establish that this model is a misconception.

Now we can introduce a better model and I use the pingpong ball in the image below with the students in the centre of the room. They are the observers on the earth and the light from the sun is coming from the left hand side in the photo.

If you go around the learner in the middle of the class making sure the “lit” face of the pingpong moon is always facing the wall on the left in this case, your students will see the same shapes we observe during the phases of the moon.

To reinforce this demonstration you could show the students this great animation by Keith Gibbs (also available in HTML5 if using an iPad).

Ok, now for the icing on the cake that you’ve all been waiting for! Check out the video below that shows a cresent moon through an infrared camera. You can see the crescent really bright, but you also see the other parts of the side of the moon facing the earth. I believe that is what is emitted by the moon in the infrared spectrum and that gets picked up by the IR camera. It is really awesome.

## Flipping arrow – awesome refraction demonstration

Posted: April 26, 2014 in Institute of Physics, Thoughts and ideas
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When @CardiffScience posted (on Google+) a video demonstration of an arrow drawn on a piece of paper that flipped direction when seen through a glass of water I knew I had to try it myself and write this post. The video below shows the demonstration which is pretty neat, but carry on readying below the video for what I think is the explanation.

As some of you might know, I am one of the Editors of Talkphysics.org with David Cotton and he posted the below photo on this thread, which is think is a convincing explanation of what goes on in my video of the flipping arrow. If you trace the path of the three rays in the Dave’s photo you can see the ray that start from the top slit from the ray box ends up at the bottom on the multimeter. This is essentially what is happening in the video, so the light reflected by the right side of the arrow gets refracted by the water inside the glass and ends up on the left when it reaches the camera. Looking at the photo above though gave me an idea, i.e. “If I go close enough to the glass I should go beyond the focal point of the glass lens and see the arrow flipping again!” – WRONG! That didn’t actually happen. However, I just noticed that Dave’s liquid was Glycerine (at least if the name of his image file tells the truth), so I wondered whether the refractive index of glycerol was such to cause less bending inside the glass, but I was wrong again. In fact, water has a refractive index of 1.33 and glycerol of about 1.47, so there should be more bending of light inside the glass. I still haven’t figured out why I can’t flip the image again if I go close enough to the glass, but I still think it was worth posting this article and if you know the answer, please leave a comment! Thanks!

## LED bridge rectifier

Posted: February 15, 2014 in Institute of Physics, Thoughts and ideas
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I have always found it is quite hard to show the path of the current in a bridge rectifier to A-level students using diodes alone. The diodes are tiny, for a start, and you end up following the wire with your finger around, but students seem to get lost in the process. I still introduce the rectifier using diodes and one thing I show them is that even using a DC voltmeter doesn’t change the sign. This is convincing for some, but it is still nice to be able to give further proof of what’s going on.

The diagram might also help, because it is easier to follow the path around.

However, I have started building rectifiers with LEDs alongside the diode version and it works a treat. The first thing I show them is the circuit on DC current. Only two of the four LED light up, so I can ask “What would happen, if I reverse the polarity?” They now seem to get it and they often answer correctly that the other two LED will light up. I change the polarity several times to simulate the two half-waves, as in the images below.

Then, I get the spinning wheel we use to observe ripples in the ripple tank (the one with gaps, I can’t remember the name) and put the LED rectifier on AC. The result can be seen in the video below.

## A nice Pressure in Liquids question

Posted: December 6, 2013 in Institute of Physics, Thoughts and ideas
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I first was introduced to this really nice question by Neil Atkin (@natkin) and ever since I have tried to find a good way of showing it. So, look at the question and the explanation that I think is correct, as far as I can tell (but please point out any faults in my reasoning). Then, check out the simple demo I used to show this.

“If I am on a boat in a pond and I hold a 10 kg rock in my hand, what will happen to the level of the water if I drop the rock inside the pond? Will the water level increase, stay the same, or be lower?”

It’s all to do with Archimede’s Principle that states that the upward buoyant force exerted on a body immersed in a fluid is equal to the weight of the fluid displaced by the body.

This should help us think about this problem. In fact, if the boat is floating it means that the weight of the water displaced by the rock when it is inside the boat must be the same as the weight of the rock itself. That is because the upthrust balances the weight of the boat, myself and the rock, or the boat would sink. So the rock displaces a volume equivalent to the space occupied by 10kg of water, i.e. 10 litres.

When I throw the rock inside the pond the water displaced by the rock is only the volume of the rock itself, which is most likely not 10 litres, but much less. So, the level of the water in the pond decreases!

I took these two photos before and after to convince you of this (the measuring cylinder we used in another attempt was to big to appreciate the difference). Click on either photo to enlarge them and see them in Gallery view.

## The Hidden Particles of Fishy Tank

Posted: May 17, 2012 in Institute of Physics, new technologies, Thoughts and ideas, Workshops
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In a previous post I wrote about the Fish Tank Cloud Chamber workshop funded by IoP and organized by Cerian Angharad in Cardiff and I promised I would run one in Gloucester. Well, this evening I did and all delegates had great fun taking part in the filming of the iMovie trailer you can see below. I made using an iPad third generation and it was very easy to do, because these trailers come with the storyboard already set up for you. In fact, all the clips, places for captions and duration of the trailer are fixed, which means that you really need to focus on the message you want to convey and do it in the simplest way possible. But it also prevents you from adding too much to your video. Also, I like the fact that there is no dialogue and the message is communicated entirely through the clips and captions you create!

These are important skills for any learner and I would encourage any educator with an iPad, iPhone, or iPod Touch to let their pupils create these short trailers for their learning. I got the inspiration for this one and other trailers I made by the inspiring work Gavin Smart does with his learners at Priory Community School.

## Fish Tank Cloud Chamber

Posted: March 24, 2012 in Institute of Physics, Workshops
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I attended the IoP make and take workshop to build my own fish tank cloud chamber last Thursday and it was a great experience! The workshop was organised and led by Cerian Angharad and held at St Teilo’s CW School. The tank is really easy to build and quite cheap too. All you need is some sticky felt, which you stick at the top (which is actually the bottom of the tank) and soak with alcohol, a plastic fish tank, a metal tray, on which the top of the fish tank needs to be stuck to with duck tape and you’re done. The rest is a normal shallow tray that can be found in most school labs, a sheet of polystyrene to rest on the bottom of the tray and dry ice that goes between the polystyrene and the tray with the fish tank resting on it. See the photo below to have a better idea!

The rod in the middle of the tank is a radioactive welding rod which emits alpha particles. The chamber works really well and you can soon see lovely traces from the  alpha particles emitter by the rod. Some of the tanks that were made also showed very clearly cosmic rays/background radiation coming into the tank from the sides.

This is one of the best workshops I have even been to and the tank is great for radioactivity demonstrations, as the whole class can gather around it and see what’s going on. I will certainly run the workshop in my area in Gloucestershire, so contact me if you are interested in attending. If you are too far from Gloucestershire, find your IoP Network Coordinator here and ask them if and when they will run this workshop in your area!

Watch the video below to get a feeling for what you will see in your tank!

I was privileged to be at the ASE Conference last week and meet so many great Science Educators in the flesh! In particular it was lovely to meet so many who regularly tweet at the #ASEChat.

It was also great to run, for the third consecutive year, my Modulated Laser Pen workshop which is always very well received and attended. This year, as usual there were quite a lot Norwegians and several from other parts of Europe, which shows again how good the conference is to attract educators from so many parts of Europe!

Coming back to the workshop, it consists in building a modulating circuit to add in series to the laser diode in a laser pointer and the whole kit costs less than £20, but the IoP provides it for all participants free of charge! The receiver is simply a small photovoltaic cell plugged into a Radio Shack mini-amp through a Jack lead. You can find the instructions to make your own and some teaching ideas in this resource I uploaded on TES (just click here). Most parts can be found from Rapid Electronics and the mini-amp from Amazon.

Another cause for celebration and enjoyment was the 10th Anniversary of the Institute of Physics Teacher Network, which has run very successfully for all that time and of which I have the privilege to be part as the Network Coordinator for the area of Gloucestershire!

## 2011 in review

Posted: January 1, 2012 in Free Resources, Institute of Physics, Mind Mapping, new technologies, NGfL Cymru, Thoughts and ideas
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The WordPress.com stats helper monkeys prepared a 2011 annual report for this blog.

Here’s an excerpt:

The concert hall at the Syndey Opera House holds 2,700 people. This blog was viewed about 21,000 times in 2011. If it were a concert at Sydney Opera House, it would take about 8 sold-out performances for that many people to see it.

Last night we had our first TeachMeet entirely dedicated to the teaching of Physics in Gloucestershire and despite the inclement weather and illnesses a few teachers from the region managed to come and give some great presentations! A particular thank you goes to Helen Rogerson (@hrogerson) who took the time to record two videos for us to watch. And that’s what we did! In fact, the TeachMeet began with Helen’s 7 minutes video which showed some great stuff she does wit their learners and parents with revision. Of particular interest to the participants was the part on Electromagnetic Induction, which sparked a series of interesting discussions and caused us to go back and watch the lovely demonstrations several times. This was indeed a lovely part of our TeachMeet that I believe stood out from others I have attended and organised in the past. In fact, it is quite easy to rush through all the presentations trying to fit everyone in and forget about allowing the participants time for discussion and to network. But last night ideas on alternative ways to use the equipment and extensions to the demos were freely flowing and created a very relaxed atmosphere from the very beginning.

Next, IoP award winner Kevin Betts showed a great demo of “Dancing Waves” on custard on the cone of a speaker. You can see his Magic in the video below.

Steve Rice was up next showing us how he uses  a sparkler attached to a drill to simulate the gravitational attraction between the earth and the moon. As the sparkler spins around the drill, the sparks fly along the tangent to the circle drawn by the sparkling tip, which helps the learners visualise what would happen if the gravitational pull between the two heavenly bodies suddenly disappeared. I liked this demonstration because it allows the learners to think outside the box and stretch their understanding in the realm of the abstract.

Below is a video of these two lovely demonstrations.

After that it was my turn to talk about how I used one of the best iPhone/iPad apps I have ever come across, the Vernier Video Physics, with my learners. You can find this resources on the TES website here. It was also the first time I publicly announced my new role as Science Lead at TES commencing in January and I explained that, although I occasionally use it already, I will actively interact with the Twitter sphere using @TESScience from then.

We closed the TeachMeet with our sponsors’ raffle, which included a very generous box full of Nelson Thornes books, ranging from GCSE revision guides to a Muncaster tome 4th edition. ThinkBuzan also offered a free copy of their Mind Mapping software iMindMap 5 Ultimate (the last two links are affiliate links, so Google iMindMap 5 instead, if you are bothered by this sort of thing).

Two other teachers emailed me apologising they couldn’t attend due to illness, but they sent links to interesting stuff that they would have shared in person, if they had been there. The first is the YouTube video below about mixing colours with glow sticks shared by Bernadette Willey.

The other tool is Poll Everywhere shared by Lewis Matheson, which seems a really neat tool to use with mobile devices!

I thoroughly enjoyed myself last night and I learnt a lot (as usual) from innovative colleagues in the Gloucestershire Network. I hope to see many more at our next events in the new year.