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.