Balmoral: a royal anemometer

There is an anemometer on the tower at Balmoral underneath the flagpole. Anemometers can measure windspeed in various ways. They can drive a generator like a wind turbine would. The faster the speed, the greater the rate of flux cutting so the bigger the induced emf and thus current. You then calibrate current against known wind speeds. Another way is to have a permanent magnet spun round by the shaft so that it passes over a reed switch once a revolution. This closes a circuit and sends a pulse of current that can be counted. A similar method would involve a light passing over a detector such as an LDR once a circuit. These methods would allow calculation of angular velocity. Wind speed then = angular velocity x radius of arm,

Electron accelerator at Diamond

The way that the electrtons for the beam are produced is actually quite low-tech and is similar to old TV sets. There is a thin piece of wire with current in it that heats up, The electrons get excited and are "boiled off" the surface. Then they are attracted by a large positive voltage from an anode. The Diamond website talks abiut a linac - a linear accelerator. Many of these use a series of alternate anodes - the voltages are made positive in front of approaching electrons and negative behind them. The website talks about RF cavities for accelerating electrons. This will be like a klystron tube in reverse - see recent post. http://www.diamond.ac.uk/Science/Machine/Components/linac.html#

Equivalence in General Relativity

I have been reading Lisa Randall's book Warped Passages. She explains with extraordinary clarity. I knew that Einstein has based his ideas for Special Relativity on the idea that you cannot feel the difference between standing still and moving in a straight line at constant speed, These are the two conditions stipulated in Newton's First Law of Motion. I also knew about the equivalence between inertial and gravitational ,mass. But Lisa Randall made it very clear to me that General Relativity hinges on Newton's Second Law of Motion in a similar way to Special Relativity hinging on the First Law. The idea is that acceleration of a mass comes from a resultant force. Or put it this way: if the car accelerates very rapidly, you feel pinned back in your seat in a way equivalent to gravity pinning you to the ground, I knew this stuff but I hadn't made an explicit connection to an equivalence in the Second Law like that in the First Law with Special Relativity.

Equal and opposite forces

Looking at this electricity pole near Oxford, it occurred to me that the heavy top wires pull in opposite directions. They are the same height so they would put the same turning force or moment on the pole (taking the base of the pole as the pivot point). A single wire would rely on the ground exerting an equal and opposite counter moment to keep it upright. There will be a lot less of the pole below the ground which means that the force exerted by the ground would have to be much bigger than that by the wire to make up for the lack of distance. Simpler to have the forces on the wires balance.

Richard of York Gave Battle In Vain

If you use the mnemonic for the colours of the visible spectrum and have wondered who Riard of York was, you can watch Benedict Cumberbatch play him http://www.bbc.co.uk/iplayer/episode/b07d3ks4/the-hollow-crown-the-wars-of-the-roses-3-richard-iii (UK only and for a couple of weeks more) To add to the confusion, he was Richard of the House of York, but in the play he is Richard, Duke of Gloucester!

What is charge?

I did this static electricity experiment with my class. In the top picture, the two different materials attract. In the bottom picture, two identical materials repel when charged by friction. This is evidence that there are two types of static electricity which were named positive and negative charge. But what is charge? If mass is that thing which allows an object to feel a gravitational force, then charge is that thing which allows an object to experience an electromagnetic force, It is that hard to define! We can say what it does but not what it is. I like the treatment on this site http://amasci.com/elect/charge1.html

Pelton Wheel at Kinlochleven

Kinlochleven was once the site of an aluminium smelter. This requires a lot of electrical energy which was generated by hydroelectricity. Thus the Pelton Wheel is a memorial to this former industry. The old smelter building is now the national ice climbing centre. Reading about the Pelton Wheel, I have learned that it is different from the wheels used in corn-grinding water mills where the water feeds in over the top of the wheel. There the water has no kinetic energy but its weight in the bucket pushes down on the wheel. Here the water undershoots the wheel. The wheel puts a force on the water to stop it moving so by Newton's Third Law the water puts an equal an opposite force on the wheel. Clever design means that if the water really does leave with no kinetic energy, the wheel's rim is moving at half the speed that the water had.

Galileo's experiment

We found this jigsaw on our cruise ship. So the story goes, Galileo used the tower to drop objects of different mass. Previously Aristotle had suggested that the heavier an object was, the faster it would fall. Hence if a heavy and a light object were dropped at the same time, the heavy one would hit the ground first. I love to show classes that a metal weight and a screwed up piece of paper hit the ground at the same time, It just seems so counter-intuitive. However, here is a bit of reasoning: Take two identical metal weights and hold them side by side. Drop them. Logic says they will hit the ground at the same time. Now glue them together. What has changed? Why would they fall twice as fast just because they have been glued together? Try this for more info https://en.wikipedia.org/wiki/Galileo%27s_Leaning_Tower_of_Pisa_experiment

More on GPS and Culloden

My friend emailed to point out that there is a more precise version of GPS called Differential GPS which is
"Where you have one or more fixed local base stations that know their position accurately and continuously broadcast the difference between their known position and the satellite predicted position.  GPS devices connected to their network can then receive the differences in real-time and apply the same correction factor to their own satellite predicted positions. This typically increases accuracy to less than a metre (with some of the better systems it can be accurate to just a few centimetres).  This type of system would work well for a fixed open-air site like a battlefield."
There are some pictures of the reference stations here https://en.wikipedia.org/wiki/Differential_GPS. We don't know if this is what they are doing at Culloden but it would certainly be brilliant for a fixed setting like this. Thanks, Pete!

Zero error at the Cross Keys Temperance Inn

We went to the Cross Keys Temperance Inn near Sedbergh - a pub without beer! This was amongst the curios hanging in the parlour...

I love the fact that it calls itself a spring balance, like the ones at school. It's also made by Salters who are still in the trade. I was interested that it doesn't read zero with nothing hanging on. We call this a zero error and it would result in a systematic error because all readings would be out by the same amount. The needle is not flush with the scale so there is a parallax error - from the angle I took the picture it looks like 12oz but the shadow suggests 8oz would be correct. The precision is stated as +/- 2oz, although you should be able to read the wide scale divisions to the nearest ounce. It claims 60lb but the max reading on the scale is 20lb. Does it go round more than once? The wonderful Cherry Bakewell might tempt me back to find out!

Klystron tube

I found this in the museum at Croome Court. It is used to generate the high power radio waves for a radar device. It involves using an electron gun to fire a beam of electrons through two cavities. The first cavity is called the buncher and uses an oscillating electromagnetic wave to change the electric field between the sides of the cavity. The field oscillates very quickly, changing polarity. One way round it accelerates the electrons and then flips to decelerate electrons. Thus the electrons end up bunched rather than uniformly spread as they go on. They then enter the second cavity called the catcher. When the field in this acts against the motion of the electrons, the electrons do work on the field and give it energy, which amplifies the wave that was causing the field. By coupling the catcher back to the buncher, you can get it to generate a wave without any input by having it amplify the random noise that was in the circuit anyway. https://en.wikipedia.org/wiki/Klystron

Nuclear power across the Solway

You can see Chapelcross power station from Wigton. It used to have cooling towers but they were blown up a few years ago. It was an early nuclear power station. Natural unenriched uranium was used. A neutron splits one nucleus of uranium-235. The split releases particles with a lot of kinetic energy. In other words, these fragments move around. Now think: when you heat something up, the particles move around more. So if the fission process splitting the nucleus makes particles move around more, they must have a higher temperature. Pressurised carbon dioxide gas was blown over the hot fuel. The heat energy went into the CO2. This then heated water in separate pipes by ,means of a heat exchanger. The water turned into steam which turned a turbine and thus a generator. Each fission releases more neutrons which hit more nuclei in a chain reaction. Slow neutrons split nuclei of uranium-235 more easily so graphite was used to slow the neutrons. The graphite here is referred to as a moderator.

Magnetic domains at Rogersceugh

We walked out onto Bowness Common behind Rogersceugh Farm and found the compass sculpture. Ferro-magnetic materials contain small magnetic areas called domains. In unmagnetised iron, the domains all point in different directions and cancel each other out so the iron cannot act as a magnet. It is possible to use another magnet to make the domains line up so that they act in unison and make the iron into a magnet. Iron is said to be a soft magnetic material because the domains can be lined up easily but can get knocked back out of line quite easily. Steel is a hard magnetic material because it takes a lot to line up the domains but they stay lined up for longer. So transformer cores are made from soft iron. The alternating current in the primary coil creates an electromagnet that lines the domains up first one way and then the other way - as shown in the photographs. It does this back and forth 50 times a second. If steel were used, the effort of switching the domains would waste too much energy.

Pond skaters and surface tension at Campfield Marsh

Mrs B spotted this little bug on a pond at Campfield Marsh. One important reason for their ability to walk on water is surface tension. Water molecules have a kind of charge separation that makes one end positive and the other end negative.This means that the molecules attract each other. A molecule in the middle of the liquid is pulled equally in all directions. At the surface, there is nothing above to pull the molecules upwards so there is a stronger net force downwards. This pulling inwards creates surface tension. Provided the surface tension is greater than forces due to the insect, it won't penetrate the surface. Hairs on the legs increases its surface area thus reducing the force per unit area so that at any given point, the surface tension will not be beaten.

Huygens' construction at Bowscale Tarn

 This is Bowscale Tarn, made famous by its mention in a poem by Wordsworth. He claimed that there were two immortal fish in it, and that attracted Victorian tourists. presumably if the fish are immortal, they are still there, but no sign of them today. However the pattern of waves on the water reminded me of Huygens' Construction.

Huygens suggested that you could predict where a wave would go next by marking a whole series of points along a wavefront and making these the sources of semi-circular ripples. Where the ripples overlap, that's where you get the next wavefront. Classes find that hard to believe, but it does work. Today the waves were being driven from left to right by the wind. From above they looked like good plane wavefronts until you magnify the picture. Then the wavefronts seem to be broken up into smaller sections, reminiscent of sets of semi-circular ripples. For diagrams and a further explanation see http://ipodphysics.com/huygen-principle.php

Drumlins in Glen Clova

Glen Clova in Angus is one of the most beautiful places I've visited. Sadly it rained so we didn't get to climb up to Loch Brandy but that gave me an excuse to look at the drumlins. Drumlins are formed by material deposited by glaciers. I had thought that they were due to galciers melting but some theories seem to favour deposition due to melt water under the glacier. If it is water depositing the particles, you'd expect the bigger lumps nearer the bottom and the finer grains to be suspended for longer. That would seem to tie in with the undisturbed sections of this excavation.

GPS on the Culloden battlefield

If you take a tour of Culloden battlefield near Inverness you are given a Smartphone device that triggers a commentary automatically at numbered sites as you walk round. It knows where you are! GPS works by having fixed satellites with very accurate atomic clocks. They send out coded signals that are picked up by the handset. This lets the handset work out how long the signal took to arrive from a given satellite. By combining time-of-flight data from different satellites of known location in space, it can compute where you are. It is said to be accurate to 7.8 metres. In other words, the locations on my tour must be over 7.8 metres apart. I'd say about 30 metres, but perhaps less than that on some parts of the tour. It would work on a battlefield but not inside a museum because the objects are much closer.

Stationary wave on High Crag

I was stood looking at Pillar Rock when I accidentally hit this old fence post with my walking pole. I got a nice note out of it. There was clearly a node at the bottom where it is fixed to the ground and cannot vibrate. There was another cross bracket attached about 80 cm up which would have acted as another fixed point or node. Two nodes with an anti-node between constitutes half a wavelength, so one whole wavelength would have been 1.6 metres. Using c = f x lambda, with speed of sound in air as 340 m/s then frequency f = 314/1.6 = 200 Hz to 1sf. That sounds about right as what I heard was nowhere near high enough to be 1000 Hz.

Demonstrating back emf in a d.c. circuit

 I set up the circuit above with two bulbs in parallel. The second bulb is wired through a solenoid coil which sits on a laminated soft iron core. With the circuit connected to d.c. the switch is pressed. Needless to say, the bulb wired on its own comes on straight away. But you have to wait a second or two for the bulb with the solenoid to come on. This is because the solenoid turns into an electromagnetic. It goes from having no magnetic flux inside it to having a high magnetic flux inside it. There is flux linkage in the coil. By Faraday's Law, an emf voltage is induced in the coil if there is a rate of change of flux linkage. By Lenz's Law it has to fight the voltage from the battery pack, so it is a back emf. Whilst it is fighting the battery pack voltage, there is a momentary dimming of the bulb. Once the circuit is switched on, the electromagnet's flux remains fixed at a high level and there is no rate of change of flux to cause a back emf. The top picture shows the second bulb just beginning to come on. Whereas if you connect to a.c, there will always be changing flux in the electromagnet and always a back emf, so the bulb never comes on. See below!

Transit of Mercury

The weather was perfect for the Transit of Mercury today and I was able to follow it from beginning to end. There was an obvious sunspot in the middle of the projected disk and it was bigger than Mercury! In fact, \I was amazed by how small Mercury is. But it was perfectly round and moved perceptibly. It was so small that most of my attempts to photograph it failed. The top photograph has it in towards the top edge above the semi-circular shadow and just right of centre. It was far better live.

Playing with colour on High Pike

I've been playing with a Casio camera. It has a function called HDR Art which seems to make hill photos look more wintery! This is possible because a digital camera is just a set of numbers assigned to each pixel based on the amount of charge released as photons of light hit that pixel. Computer software can play with those numbers. Information suggests that the software plays with the contrast - this could be accentuating the difference between numbers. It also increases colour saturation. This means increasing the intensity of the colours. This means giving them a brightness above their natural level. Apparently a colour intensity of zero means a shade of grey.

Resonant cavity magnetron

Radar works by sending high energy pulses of radio waves. I found this in the museum at Croome. It was used in wartime Allied radar devices. A resonant cavity in this case refers to the idea of reflecting electromagnetic waves back of one side of a cavity. They interfere with the incident waves and can set up a stationary wave in the cavity if the width of the cavity is an integer multiple of half wavelengths. I have read that electrons are whirled around inside the device, which is a vacuum tube, and go past the openings of a series of cavities, in which they excite waves. This is all very new to me so more research needed.

SHM on the M74

I loved the SHM number plate. SHM in Physics is Simple Harmonic Motion. It is basically oscillatory motion like a mass bouncing up and down on a spring. The definition states that during the motion, the acceleration is always proportional to the displacement from equilibrium and that the acceleration is always directed towards equilibrium. In English, this means that if you pull a mass on a spring twice as bar from its natural length, its acceleration will be twice as big and pulling towards the middle. In the middle, the acceleration will be zero but its momentum will carry it through. Above the middle, it keeps going up but the acceleration will be pulling back down towards the middle.

GCSE revision: transformer efficiency

We actually made the transformers today. The a.c. caused the primary coil to become an electromagnet with an alternating magnetic field, first going one way inside the iron and then the other way. This meant that the electromagnet was turning on and off at a frequency of 50Hz. We could hear it humming. This wastes energy and makes the transformer less efficient. The wires heated up because of their resistance. This makes the transformer less efficient. The core is made from SOFT IRON which means that its magnetic areas called domains can be switched around very easily. If they weren't it would waste energy because the magnetic field needs to change direction with a frequency of 50Hz. The iron core was made of laminated strips. An odd thing is that the changing magnetic field can induce currents in the iron as well as the secondary coil, which would waste energy heating the core and make the transformer less efficient. Laminated sections reduce the effect of these induced currents which are called eddy currents.

Brilliant quantum physics double slit animation

I've been sent this link from one of my former students https://www.youtube.com/watch?v=fwXQjRBLwsQ&feature=youtu.be It explains brilliantly why electrons are said to behave as both particles and waves, giving the experimental evidence. It's also only 5 minutes long. Go on, you know you want to!
Thanks, Christine!

Squall on Chanonry Point

We drove out to Chanonry Point on the Moray Firth to see the dolphins. We had to wait whilst a squall blew through. The sea had been flat calm beforehand. Squalls come with very localised strong winds. It occurred to me that the strong wind section must move round as a block under the clouds. How does that happen? I think it will be that squalls are the result of intense convection because they often come with hail or thunder. The strong winds associated might then be the cold air descending. But what interests me is the way that this unit moves through a tranquil space, stirs it up and then leaves it tranquil again. It's a bit like a wave motion, like a carpet ruck being kicked through.