Covering the full spectrum

We went to the Greenbelt Festival on Cheltenham Racecourse. They had set up flags in the grandstand seats. I imagine it shows that the festival covers the whole spectrum. What I liked was that they used more than the traditional 7 colours. I have heard it said that Isaac Newton was superstitious about numbers and wanted 7 colours because 7 is the perfect number. So if you've ever wondered why you find it hard to see the differences between blue, indigo and violet... The spectrum shown above is arguably more realistic. I also liked it that the wind only ruffled the flags in certain seats, showing a complex air flow around the stand. If I ever get to watch the races from the grandstand, I'll choose one of the seats that was calm.

Noctilucent clouds

If you didn't see yesterday's NASA astronomy image, you MUST click this: http://apod.nasa.gov/apod/ap130819.html I'm now on the look out for noctilucent clouds!

A book about why the world is as it is

I've just read this book and enjoyed it a lot. Jared Diamond has written an investigation into the history of the world based on scientific explanations of causation. He asks why it is that Europeans conquered the Americas rather than Aztecs or Incas conquering Europe. You might say it was obvious: they didn't have the technology - but why was that? He starts by analysing the development of farming. He concludes that if you take Europe and Asia as one block - Eurasia - there were far more species of plants and animals that were capable of being domesticated than in other regions. This made us farmers earlier than on other continents. Close association with livestock means you get their infectious diseases. Eurasians developed more infectious diseases which they took with them on their conquests. Geography has its part to play. Eurasia is orientated east-west rather than north-south as in Africa or the Americas. This means that the climate is similar along the latitude and plants adapt easily in new countries. Agriculture means higher populations so they are more possible inventors so technology proceeds more rapidly. One issue in Physics is that it has a very "dead white men" European feel to its history and practice. This book goes some way to explaining that past - though it doesn't mean that the future has to resemble the past now that we understand. A final coda is about why Europe overtook China is terms of technological advance around the time of Galileo. I won't spoil it - you'll have to read the book. It's easy to read but a little over long in that he keeps repeating himself. That said, it means you can dip in as chapters become quite self-contained. He is very persuasive. Is it too good to be true? I don't think so, but I'd like to hear academic criticism of his findings.

Torque Lego style

Mrs B has been making Lego models with a kit lent to us by one of our friends. Here is on of the models that she has made.

 

 

We got the motor going and it does go forwards nicely. The motor drives two flexible rods that each drive a wheel. So the motor delivers torque to the wheels. Torque is a concept that seems quite slippery. Books and exam papers use the words moment and torque interchangeably quite often. I thought I'd boiled it down to the idea that torque is what produces pure turning but that you couldn't really use torque for something that causes a cartwheeling motion. I got this from usage of the words on exam papers. But perusal of Wikipedia. suggests something different, although acknowledging the semantic difficulty associated with the two words.

 

When a torque acts on something, it makes the mass the move accelerate, so we would say that there is a rate of change of angular momentum, angular because it is turning in a circle. If there is no change in angular momentum, then there is no torque. So a turning force that acts but cause no motion can't be called a torque. A torque is a motive force.

 

Below are photographs of how the torque is delivered from the motor to the wheels.

 

The kit came from Oxfam in Wigton originally. A great place to shop!

The UK's first aluminium plant

There is an amazing gorge and series of waterfalls at Foyers on Loch Ness. I'd never heard of it but it was one of the top three sites to visit in Scotland 250 years ago apparently. Robbie Burns, Wordsworth and Dr Johnson all visited.

 

 

So when it came to setting up the first aluminium smelter in the UK, it was an ideal site. Aluminium is more reactive than carbon, so you can't use a reaction with charcoal to reduce aluminium oxide to pure aluminium metal. Instead , electrolysis is used. The aluminium oxide is melted, which takes a lot of energy, and then electrodes are placed in it. The first plant in the UK was built in 1896 and is shown below. The only way to power it in those days was hydroelectric power, which is why it was put in at Foyers.

 

Water is collected in the village at the top of the hill, as shown in this picture. It then flows through pipes to the factory on the lochside. The gravitational potential energy is converted first into kinetic energy and then this is converted into electrical energy by a generator. The factory shut in 1967.

 

 

I loved this quotation from Lord Kelvin, the renowned Victorian physicist.

Diffraction on Loch Ness

We stayed at Foyers on the south side of Loch Ness. This photograph was taken looking north up the look from the mouth of the River Foyers. Note the shingle bank.

 

 

The exact end of the river is shown here - a gap between two shingle banks. Waves were being driven up the loch by the wind. They were straight wave fronts - what we call plane waves. When they went through the gap, they became semi-circular.

 

When plane waves go through a gap and become semi-circular, it's called diffraction. It is supposed to be most noticeable when the gap is the same size as the wavelength. Here the gap was much bigger than the wavelength. This could actually be an example of refraction. The water would be much shallower on the edges near the shingle so the water would move slower due to greater friction from the bottom. Those edges of the wave would go slower and get left behind, which could also account for the semi-circular shape.

Melvyn Bragg on the Braggs

I posted before about a Radio 4 programme by Melvyn Bragg about the Braggs last November. Since then I've met Professor Mike Glazer, who put him up to it. Professor Glazer has done a lot to remind the world of the contributions of William Henry Bragg and Laurence Bragg to X-ray crystallography. It is coming up to the centenary of the discovery and their joint Nobel Prize. Melvyn Bragg, an old boy of the school, has done another programme about them, having found out that he is indeed a distant relative. William Bragg was born 5 miles from here! Here's the link to the programme. http://www.bbc.co.uk/programmes/b0383vb0 The original programme from November is still available http://www.bbc.co.uk/programmes/b01p0s9s

Dolphins and stationary waves

We were up in the north of Scotland and went to see the dolphins at Chanonry Point on the Moray Firth. It is a narrow spit over a mile long that sticks out into the estuary. There's a road down it and a golf course, but it narrows to a shingle spit shown below.

 

 

On the rising tide, there is water coming in from the sea on your left. Meanwhile, river water is going out to sea from the right. The result is a stationary wave. It can't quite be the classic case that I teach about when the two waves are in opposite directions with same speed, frequency and amplitude, but you do get a wave feature that stays fixed in the same place on the sea. The waves go up and down but don't go left or right. You can see it as white water above the crowd in the picture above. It is clear on the water in the picture below.

 

The current carves a deep channel just off the end of the spit and the resident population of bottle-nosed dolphins gather to feed on salmon on the rising tide. Huge crowds gather to watch the spectacle. We saw at least a dozen dolphins, some of which are shown below. They performed as well, jumping clean out of the water. It is said to be the best place in Europe to see dolphins from the land. They can be as close as a few metres. You ought to go. If you don't like dolphins, go for the waves.

Durham Cathedral Bells

We visited Durham Cathedral today to visit the bells. Everyone we met was really nice. Here's a picture of the tenor bell, the heaviest. It's 28 cwt (that's short for hundredweight) - bell ringers like old units. 1 cwt is worth 50kg (2sf) in the UK, so the mass of the bell is 1400kg, which is 1.4 tonnes. That might be the mass of a small car. It took two people to ring the bell round so that it was upside down like this, but one person can them comfortably ring it because of the large size of the wooden wheel to which it is attached. The bigger radius means that the required moment to turn the bell can be achieved with a smaller force, since moment = force x distance.

 

 

Here are some clappers. The middle one was biggest. It was about 1m long with a 5cm diameter. Cross-sectional area is pi x r-squared so about 0.002 square metres. The volume is then 0.002 cubic metres, with the mass of the ball to be considered as well, of say radius 10cm, giving an additional volume of 0.0005 cubic metres. Total volume is 0.0025 cubic metres. I think bells contain a lot of copper, which has a density of 8920 kg per cubic metre, giving the clapper a mass of 22kg. This must be an underestimate! I'll go and think about it.

 

 

Here's the view down through the hole in the trapdoor to the ground floor. This is what 60 metres looks like!

 

Here are a couple of views from the top of the tower to show how high we were.

My TV aerial

 

After thinking about yesterday's post, I went up into the loft to look at my TV aerial. Sure enough, the elements are horizontal. Apparently that will be the direction of the electric field in the electromagnetic wave. Internet research tells me that this is a Yagi-Uda antenna, after the Japanese people who invented it nearly 90 years ago. The actual detector is the bit that the wire is attached to. The horizontal bits in front affect the field in such a way as to make the aerial directional. You can't see out of the loft but my gut feeling is that it might be pointing more towards Sandale transmitter than Caldbeck! The bit nearest to us on the picture is the reflector. The dipole detector is actually 2 separate sticks of metal with a small gap between then inside the junction box with the wire. The electromagnetic wave makes electrons in that wobble so the signal is detected and then amplified. In theory, the dipole aerial is half a wavelength long. I measured it as 20cm, which would suggest 750MHz waves using the wave equation c = f x lambda. Wikipedia quotes Caldbeck as up to about 500MHz. In theory, a longer dipole might be better. I studied this at university 27 years ago and reading the work on the Internet, it does sound familiar but I'll need to read up more to make sure I'm getting this right.

Caldbeck Transmitter

We went to Watchtree Nature Reserve on Sunday. I took this picture of the Caldbeck Transmitter through my binoculars.

 

I looked up the relevant details. Apparently it is 337 metres high, making it the third tallest structure in the UK. Wikipedia has details of the frequencies at which it broadcasts http://en.wikipedia.org/wiki/Caldbeck_transmitting_station Another site claims that the electromagnetic waves are horizontally polarised. I need to be more inquisitive about the local Physics features!

Transformers

We stayed at the Ski Station at the start of Glencoe, just round the corner from where they filmed for Skyfall. We found this transformer that steps down the voltage from 11000V for the Kingshouse Hotel. In the background is Buchaille Etive Mor, possibly the most photogenic mountain in Scotland.

 

 

This is the plate that tells you that it is 11kV.

 

 

Transformers are two coils wrapped around the same iron core. The primary coil acts as an electromagnet and magnetises the core. The mains electricity is alternating current, so the magnetic field in the core varies as well. This varying field induces a voltage (strictly an EMF) in the secondary coil. The size of this secondary output voltage depends on the ratio of turns between the two coils. In this case there will be a lot fewer turns on the secondary to reduce or step down the voltage to safer levels.

 

You can find out more about our electricity supply from this marvellous link: http://www.pylonofthemonth.org/

 

Pylon of the Month was one of the first things to "go viral" on the Internet around the Millennium. It has been revived by another Physics teacher. Respect!



Inside the Diamond

Last December I went on a tour of the Diamond synchrotron. Here's a photograph of the model inside. The smaller circle on the left hand side is where they accelerate the electrons up to speed before sending them around the main circle.

 

This photograph is taken inside the facility, stood on top of the main circle.

 

The electrons don't in fact go round in a perfect circle. They go along a series of straights and are then bent at corners. The yellow line on the floor shows the path of the beam.

 

 

The sort of magnet arrays that bend the beam are shown in the model photographed below. To change the motion of the electron beam in this way means that a beam of high energy electromagnetic radiation is released. This comes out as high energy X-rays, which carry on in a straight line when the electron beam (yellow line) changes direction.

 

 

The X-rays go straight on into facilities called huts. Experiments are set up in the huts. The X-rays go through samples to show, for example, the structure of a protein.

 

Diamond has a brilliant website. Here's a link to the education bit http://www.diamond.ac.uk/Home/Teachers.html . There are open days. Their staff were brilliant!

Ancient and modern

Here are some pictures taken from the Ridgeway, one of the most ancient travel routes in England. We were on Bury Down looking north across the plain to Oxford. It's a very physics-y landscape now. On the left is the Diamond synchrotron, where they accelerate electrons around a ring to generate high intensity X-rays with the aim of discovering the structure of molecules. It is part of the Harwell site, where a lot of research into civil nuclear power was done. On the right is Didcot power station.

 

I used the fact that the quantum efficiency of the charge coupled device (CCD) on the back of a digital camera (at 70%) is much higher than that of old-fashioned film (at 4%). I was able to take the following photographs through my binoculars. You wouldn't be able to do this with an old-fashioned camera because the optics of the binoculars reduce the intensity of the light. Only 4% of photons entering the camera are recorded anyway, so 4% of fewer photons makes for no picture. As you can see, 70% of fewer photons produces a decent image.

The physics of a christening

I went to a christening down south. There had been a service before hand and the air was heavy with incense. Looking up I saw was reminded that light travels in straight lines! It's like using a little milk in water to show up a laser beam.

 

 

The font had a heavy carved wooden cover on it. You might be wondering how it comes to be hovering in mid-air in this photograph.

 

The answer will lie in the metal cross shown in this photograph. I would imagine that it will have the same weight as the wooden font cover. They are at opposite ends of a chain which hangs over a pulley. When one goes up, the other must come down. Hence as you do work lifting the font cover, gravity does work on the cross to lower it. The only energy needed in the system is that required to overcome the friction of the chain and the pulley. It becomes easy to lift the heavy wooden cover.