Cromaty and the shipping forecast

 

This is a picture of the cliffs at the entrance to the Cromaty Firth, as seen from Hill 99 in Culbin Forest. Cromaty is an estuary up past Inveness but is best known as one of the sea areas on the Radio 4 Shipping Forecast. It might seem outdated now but the idea of putting storm warnings for ships out on the radio was a revolution in 1911. It must have saved a lot of lives in the century since. This use of radio waves is another example of Physics making the world a better place.

Liquid drop analogy

Here's the rain running down the window of the bird hide on Lamb Island at Threave. It was a good place to be during the shower - but at least the sun came out later. It reminded me of the Liquid Drop Analogy in Physics. I teach that if you get an electron to join a proton, you get a neutron. This is called electron capture. So in some way, a neutron could be thought of as a proton and an electron stuck together. It makes sense because a neutron is a tiny bit heavier than a proton and also that beta-minus decay is like the glue coming unstuck as a neutron changes into a proton by spitting out an electron. However, if you look inside a neutron, you won't find a proton and an electron. It's like 2 raindrops running into each other. Sure, you get a bigger drop but if you take the bigger drop apart, you won't find two distinct small drops. The analogy is that the neutron is like the big drop made when the two smaller ones join up. Oh, and the Blue-winged Teal wasn't there!

Cap cloud in the Cairngorms

 

We saw these really impressive cloud formations over the Cairngorms when we were driving back from Inverness. I think they are likely to be a huge version of cap cloud. There was a lot of snow on the tops of the mountains making it far more likely that the water vapour condense out into cloud at that level. Then winds blow the top flat. I have seen it before in the Lake District where the cloud evaporates away as soon as it leaves the cooling effect of the top, so the formation never seems to move. Hence cap cloud.

How far away is Morven?

 

We were in the Culbin Forest near Nairn on the Moray coast of Scotland. We climbed the tall viewing tower on Hill 99. You could see Morven, a prominent hill that is a long way up towards Wick. The panel board tells you its height, which works out at about 700m. If my finger blocks off 1 degree of view, I'd estimate Morven at 0.5 degrees. That works out at about 0.009 radians. The distance to Morven is then 700/0.009 = 80000m or 80km. I measured it on the map as about 70km so the method isn't bad. It's not quite 50 miles.

Axions from the dark sector at Tullie House

We went to Tullie House on Thursday night to hear Dr Laura Kormos and Dr Ian Bailey from Lancaster University lecture on Particle Physics. Dr Bailey was talking about Dark Matter. What he said was that we need to look for fields and interactions that are similar in some ways to the 4 interactions that we study at A Level but are different. We may not yet have found them because they are at such high energy. The plot in the photograph shows where they have looked so far. What he is looking at is the idea that a photon could change into a darks sector photon. Photons can't get through opaque matter because they are the force carriers for the electromagnetic force and so interact with the charges in the matter. However, a dark sector photon won't feel charge so it won't notice the solid wall. He is trying to get photons to go through solid walls from one box to another in the hope of showing that something must happen in the middle, and that the something might be dark sector particles. Thanks to both Tullie House and Lancaster University for putting this on, and it was free! And we were fed ice cream! The best feature was that the lectures were not dumbed down in any way.

Upper Sixth Estimation Question #3

If I move my hand through 90 degrees in the Earth's magnetic field it goes from having full flux linkage to no flux linkage. Suppose I make that movement in 0.1s. An emf will be induced. Your job is to look up the strength of the Earth's magnetic field and make other estimates to first calculate the induced emf. Then you need to think back to last year's work on resistivity, make some more estimates and work out the resistance of the ring. Finally you need to calculate the current that flows in the ring when I move my hand like that. Should I be worried?

 

Lower Sixth Estimation Question #3

Below are 3 views of the cliff on a hill called Roseberry Topping near Middlesbrough. You need to calculate the speed at which a rock would hit the ground if it was dropped over the edge of the cliff. You can use ideas of potential and kinetic energy, or use the equations of uniformly accelerated motion, depending on what you have been taught. You will have to estimate at least one of the numbers - say how you guessed how big it was from the photographs.

 

Warming my vacuum flask

 

My flask needs to be warmed with boiling water first before you add the hot coffee. This is because the inner metal walls would be colder than the coffee. If there is a temperature difference then there will be conduction into the walls. There is actually a double wall with a vacuum in between. There are no particles in a vacuum so it cannot conduct. The walls are shiny silver because silver is a very bad emitter of infra-red heat radiation. Heat radiation would be the only way that thermal energy could be transferred across the vacuum. Now look carefully at the top picture. You can see hot water vapour coming out of the top of the flask. This is a problem for two reasons. The first is that evaporation cools a liquid by removing the particles with most energy. The second is convection. The air above the liquid is warmed. It expands, becomes less dense and floats. There needs to be a hole in the top to let liquid be poured in and out, so it is blocked with a thick plastic stopper. Plastic is an insulator, so even if the convection heats its underside, the thermal energy will conduct up through it slowly. My coffee was still hot at lunchtime!

Rotating compost bin at Sizergh Castle

 

One of these came up in an exam question and then I found this real live example. Here the heat is generated internally by the bacteria that are causing the kitchen waste to decompose. This is done by aerobic respiration, in which glucose and oxygen are converted into carbon dioxide and water. It is an exothermic reaction so thermal energy is released. The bacteria work best at 37 degrees Celsius. The insulation means they don't transfer too much heat to the surroundings in winter and cool down. The handle means that even bacteria at the bottom can be given a turn with the oxygen. If more bacteria are participating in the aerobic respiration, the compost will be made much sooner.

Micro hydro-electric scheme in Ennerdale

 

This wooden shed in the woods contains a micro hydro-electric scheme to power the Field Centre at Low Gillerthwaite. Apparently it had previously used diesel generators. I'd guessed what it was because I could hear it humming but inspection revealed a pipe coming in down the hill which joins in the middle photograph. Then we found the outflow in the bottom photograph. It said 1000V AC on the door. Internet research shows that it generates 5kW at peak flow. That's basically 2 kettles at once! At peak flow it would be 5A at the generator. Thinking about it, since output emf is proportional to rate of flux cutting, you'd only get 1000V when it was turning fastest. I've never really thought about these naturally powered generators producing different voltages at different times. That will some research. If you want more details on this scheme, try http://www.bre.co.uk/renewabletechnologies/filelibrary/casestudies/Low_Gillerthwaite_Field_Centre.pdf

Apparent depth in Ennerdale

 

Look at the crystal clear waters in upper Ennerdale. They are deeper than they look. The light coming up from the stones at the bottom speeds up as it enters the air, which is optically less dense than water. It therefore bends away from the normal line. Our brains cannot cope with the fact that light has bent. We think it has gone straight. The diagram below shows with an X where we think the fish would be - not as deep as it actually is. The water will be deeper by a factor dependent on the amount of bending. This is called the refractive index. The refractive index of water is 1.33 so the water will be 33% deeper than it looks.

 

Triangulation in the Rhins of Galloway

 

 

We climbed up to the monument above Leswalt in the Rhins of Galloway. It's an excellent viewpoint, looking out over the sea to Ireland and back across Loch Ryan to Stranraer. That's why there is a trig point up there. I've blogged before about benchmarks and their use in map making. The Ordnance Survey apparently started putting in triangulation pillars from 1935 onwards. That's much later than I thought. The aim is to be able to see 3 other pillars from the one you are at and to measure angles and distances. Height can be done by measuring angles up and down as well. So somewhere in the photographs there is probably another trig point, but I don't know exactly where to look!

Polarised light from a laptop screen

 

Here's the proof that laptop screens produce polarised light. These polarising sunglasses are twisted through 90 degrees and the view goes from dark to light. I need to look at how a laptop screen works to find out why the light is polarised, but it looks as though the polarisation might be diagonal across the screen.

Reactivity on Roseberry Topping

Roseberry Topping is an amazingly shaped hill that overlooks Middlesbrough and Teesside. The crag on the end was formed when the end of the hill collapsed in 1912. This was because they were mining underneath. If you look carefully at the bottom picture you will see that there are thin layers of shale dividing up the sandstone. The shale is very weak - you can pull it out with your fingers. No wonder the rock collapsed. They were mining for iron ore. There are rust coloured deposits in the second picture. The iron ore was taken to Teesside where it was smelted in blast furnaces. Smelting works because carbon is more reactive than iron. Reactivity in metals is to do with how easily they can lose electrons. The Group 1 metals like potassium and sodium lose their outer electron very easily so they are the most reactive. They are more reactive than carbon so they can't be smelted. They have to be extracted by electrolysis which is expensive. The more stages in the extraction process, the more expensive the metal.

Opaque: Grouse Butts on The Cheviot

 

We climbed up onto the shoulder of The Cheviot, the highest hill in Northumberland. It is a managed grouse moor - there were birds everywhere. Come August, people will pay to hide behind the wooden screens you can see to shoot the grouse. The wooden screens are called grouse butts. They are obviously opaque, because you don't want to be seen by the grouse. But what makes a material opaque? I was reading that metals have energy band gaps between their electron energy levels of the order of 1 eV. This would give a wavelength of  1200nm which is infra-red. The theory is that these band gaps will include the visible wavelengths, so visible light will provide energy to get electrons up into the next band. The light is absorbed so metals are opaque. Non-metals like diamond have much higher band gaps so don't absorb visible light. What about wood? Not sure, but the molecular structure is very different being made of polymer chains.

Brilliant scale model of the Solar System

I was sent this link http://joshworth.com/dev/pixelspace/pixelspace_solarsystem.html You ought to try it. It sets up a scaled diagram of the Solar System based on the idea that the Moon is the size of one small pixel on your computer screen. You have to scroll right with the right arrow on your keyboard to navigate out through the Solar System. It gives a clear idea of just how empty the Solar System really is. I love the humour. Apparently the number scale along the bottom works in Google Chrome but not Internet Explorer. Have fun!

Coal lorries

I often use the idea of coal lorries to explain electric circuits. I say that the lorry collects coal at the battery and delivers it to components in the circuit such as bulbs. I like the model because it gets across the idea that charged particles like electrons carry the energy. They are not themselves the energy. When I started teaching it was common for students to think that electrons were used up in a bulb. This model gets round that idea. It helps to explain the sharing of voltage in a circuit by talking about the number of bags of coal delivered. Just don't mention the idea at a gathering of Physics teachers ... it caused a scene over dinner a couple of years ago! The weakness of the model is that it would suggest a time lag when you turn on a switch before the electrons arrive at the bulb. But actually electrons start moving at all points in the circuit at the same time. This can be show by having a long loop of rope and getting students to feed it through their hands. They are both models. Models help understanding but have weaknesses. Being able to identify and explain weaknesses really helps understanding, so I won't be giving up on coal lorries.

Stevenson screen at Threave

Here is an old-school weather station on the National Trust for Scotland Threave Estate near Castle Douglas. The white box is called a Stevenson screen. Inside it are thermometers and pressure gauges and instruments like that. The box stops direct sunlight so infra-red heat radiation can't affect the thermometer readings. It also keeps out rain and snow for similar reasons. But the slats let the air circulate to give perfect conditions for shade temperature readings.

Not the Shrove Tuesday pancakes - my waffle maker...

 

In a break with tradition, we made waffles instead of pancakes yesterday. I have photographed our waffle maker. You plug it in so that the inside top and bottom surfaces heat up. Then you pour in a ladle full of batter. You drop the lid down so that it spreads out on the hot surfaces. It got me thinking about the method of heat transfer. The surfaces are touching the batter so it must be by conduction. It takes a couple of minutes to cook through because the batter is not a particularly good conductor. There is no air space inside to allow for convection or heat radiation. It is possible that there will be a small amount of convection from the bottom surface into the batter at first whilst it is still liquid but once it has cooked enough to solidify thermal energy can only be transferred by conduction.

With James Clerk Maxwell in Galloway

 

By chance we found the grave of James Clerk Maxwell in the village of Parton beside Loch Ken. What a beautiful place! If you haven't heard of Maxwell, he is one of the most important physicists ever. He's up there with Einstein, Newton and Galileo. It's just that the maths is less accessible. He developed the theory of electromagnetic waves. There will be more to come on the more accessible parts of this work. If you go to visit, note that the grave is in the remains of the old church. I think his father helped to design the new church (kirk). The monument with the plaque on is by the war memorial in front of the church.

Multiple shots and exposure time

 

 

Today I used the multiple shot function on my camera. It takes 5 pictures automatically in quick succession. Here are the first 3 pictures. This means that the exposure time must be about 0.3 seconds. This means the EV is log to base 2 of 2.8 squared over 0.3 = 4.7. That's a higher EV than the manual claims!

Exposure time on a cheap digital camera

Look at the streaks of white where the snow was falling yesterday. It's a view of Grasmoor from Fleetwith Pike. It occurred to me that if I knew the exposure time I'd stand a chance of working out the speed of the snow by estimating the length of the tracks. I found an online camera manual which said the shutter time was between 3EV and -3EV. Detective work says that EV stands for Exposure Value. EV is calculated as Log(base 2) of F-number squared divided by exposure time. More on some of this later, but the F-number on the front of the camera is 2.8. The problem is that the camera automatically sets the value. It can't be 0EV because that calculates out at an 8 second exposure time. If it has set itself to 3EV then the exposure time is 0.98 seconds. But I suspect it is less than that because for example a photograph of the second hand on a watch would be blurred. I need to do some thinking about this.

Dissipating heat in Warnscale Head Bothy

 

This bothy took some finding but the view was awesome. We cooked our lunch there. The hot pan and the hot kettle were fine to put back in my rucksack after lunch but had been hot enough to burn me earlier. So what happened to the heat? Thermal energy makes atoms wobble more. The atoms in the pan are wobbling violently and that gets atoms in the surroundings wobbling. But there are so many more atoms in the surroundings that each one only gets a very small share of the extra wobble ... so little extra wobble to each one that you can't even tell that their temperature has gone up. We say that the thermal energy has been dissipated. And notice that the pan, the kettle, the stone floor and the air all end up at the same temperature. We say that they are in thermal equilibrium with each other. We did our best but I think that the person who wrote in the visitors' book that it was "b------- freezing" wouldn't have been impressed. But thanks to the MBA people for looking after the bothy so well! It was in great condition.