Nine o'clock Oxford time

I had a room opposite Tom Tower in my second year. The bell rings 101 times at five past nine in the evening which was a nuisance at times! I understood that it was to summon the students back in for the night but I could never understand why five past nine. It turns out that it is a result of G.M.T. When the railways made a common time for the UK vital to keep trains running on time, the idea of using the Sun highest in the sky in that town as noon went out the window. Time was now fixed by noon at Greenwich. Noon at Greenwich is five minutes ahead of Oxford, so by ringing at five past nine G.M.T. the bell was still being rung at the true 9pm local time.

Brilliant programme about Einstein

To celebrate 100 years of General Relativity, the BBC have made a great documentary. Here's the link http://www.bbc.co.uk/programmes/b06s75vs It will be valid for a couple of weeks.

Max Min Thermometer

 I got a wonderful present from Mrs B at the weekend - a Max Min Thermometer. This is also known as Six's Thermometer after its inventor. It is a U-shaped thermometer which records the same temperature on both sides. If you look carefully you'll see that the number scales go in opposite directions on each side. Each side also has a small steel marker in the tube. These record the maximum and minimum temperatures in a given time period. They stay where they are and you have to use a magnet to pull them back to the end of the coloured liquid to allow the process to start again.

 It works because there is a clear liquid in the tube that records the minimum temperature (left hand side above and right hand side below). This expands and contracts with temperature pushing the blue temperature recording liquid round. Above the blue liquid on the other side is a vacuum - nothing to stop the blue liquid moving round the tube.

Earthshine - lighting up the Dark Side of the Moon?

Look at this picture of a crescent Moon, taken around dawn. The bright crescent is all we can see of the half of the Moon that is facing the Sun, given the angle that we are viewing from. You'd think that the side facing the blackness of space would be dark. But you can see it because sunlight reflects from the Earth back up onto the Moon, lighting it dimly. It's like the full Moon shining on Earth - that was bright enough for us to walk in the hills last year. Now I am aware that the phrase Dark Side of the Moon doesn't mean the side out of the light - that's another story - but it sounded nice in the title!

Isaac Newton's prism experiments at Woolsthorpe

I had my "fan boy" trip to Woolsthorpe - as close as it comes to visiting a shrine in Physics! The top picture is the window that Isaac Newton used for his light experiments. A later owner enclosed that part of the room so these days light can't go as far as it did in Newton's diagram. I knew that he had used one prism to split the white light into a spectrum and another to pull it back into a white light. I was only vaguely aware of his other experiment: he took the spectrum and used a slit to take only the red light which he then put into a second prism. Only red light came out of the second prism. He was intent on disproving a theory then that light was colourless and that the glass itself gave the light all the colours of the spectrum. Each experiment shows that the glass is not adding colour. I need to read more about the nuances of why both experiments were considered necessary.

Making measurements with Searle's apparatus

We have been using Searle's apparatus to gather data that we will use to find the Young Modulus for steel wire. It is the same sort of scale as on a micrometer screw gauge. The vertical scale on the left hand side is measured in mm from 0mm to 10mm. One complete turn of the central barrel moves the leveling apparatus by 0.50mm. You start by taking a reading on the left hand vertical scales using the top of the rotating barrel as your marker. The problem is that it takes two complete rotations to move the 1mm between scale divisions on the vertical scale. So you have to make a decision about whether you are below or above 5.5mm for the situation shown in the picture.I think we are below, so we take 5.0mm and add the reading from the barrel, taken where it meets the vertical scale. It is 36 to the nearest whole number. Hence the reading is 5.0 + 0.36 = 5.36mm.

Planets in line and the ecliptic

This was taken on Tuesday morning. The Moon has since disappeared but as well as Venus along the diagonal line with the Moon in the photo, I was able to pick out Mars and Jupiter this morning. They are all in a line because they are all in the same plane in orbit around the Sun. The dust and ice from which the planets formed was pulled into a single plane as the Sun rotated in its formation. The line up in the sky is called the ecliptic. So why do I see them along a line at 50 degrees to the horizontal and not along a nice horizontal line? In part, it's because the Earth doesn't sit properly upright. It is at an angle of 23 degrees to the ecliptic. I then tried to work out how much of the rest is because of the latitude. Wigton is about 54 degrees north so we are standing at an angle to outer space! The 3D geometry is beyond me tonight.

Gales in Wigton: what causes the wind?

Gales in Wigton again today! One of my classes asked me what causes wind. The answer is basically convection. Hot sunshine on the Equator makes air expand, become less dense and float upwards. What goes up must come down. In the Northern Hemisphere it comes down over the latitudes of the Sahara desert. Then at ground level it flows back to the Equator. There is another cell like this taking air up from Europe and down over the Arctic. It is symmetrical in the two hemispheres. It is the joing up at ground level to complete the loop that gives us our winds. They don't go north/south because of the turning Earth but that's another story.

Measuring Storm Desmond in Wigton

I posted the picture above a couple of years ago to show the base level of the Wiza on Station Road. I took the picture below on Saturday afternoon. By comparing the two, the water level is 1.9 metres higher.

I hadn't thought to empty our bucket rain gauge in the garden ahead of the deluge, so this is what collected in a Wigton garden over the last 2 weeks:

That's about 180mm. Nearly twice that fell in a day over the highest ground in Cumbria.

Angular velocity at Isaac Newton's house

I finally made it to Isaac Newton's house at Woolsthorpe in Lincolnshire. This exhibit was in the science centre. You push the ball round the circle and it decays into the centre. I am thinking about the shape. If it represents gravitational potential in the Solar System, then perhaps it is a 1/r shape. The photograph exposures should represent equal time periods. Thus we can comment on the angular velocity as the ball moves from the outside to the centre. In the top photograph, it manages 90 degrees. By the second photograph, the trace of the ball is twice as long - the angular velocity has doubled. In the final photograph, it has doubled again to complete a full 360 degrees. It is true for the Solar System that angular velocity is bigger closer in. I will look in to making measurements of radial distance from the photographs to quantify the relastionship.

Meine Tasse ist in der Einleitung von Physik im Advent

Sie müssen die Filmen von Physik im Advent zusehen.  http://www.physik-im-advent.de/index.php?language=de&MODsid=utjljpou0jlq0oqloborvo44p5 Da können Sie meine Tasse sehen. http://wigtonphysics.blogspot.co.uk/2015/11/verdunnen-schwerkraft-auf-meine.html

Isaac Newton and the Wigton floods

I was fortunate to be able to go to Isaac Newton's house at Woolsthorpe near Grantham at last. His most famous work is the Principia Mathematica. What I didn't know was that the middle section of the book was about fluid mechanics. And the pictures below show a body of fluid in Wigton today...

Apparently Newton wrote about the effects of friction and viscosity on the flow of fluids. At the edge of the river, friction from the bank acts on the water, slowing it down. Then he modeled the water as moving in layers, each one affected by the pull of the one outside it. This pull of a liquid is called its viscosity. Hence the fastest water flows in the middle. So important was the work that they now talk about Newtonian fluids. I used to know about these things so I need to re-read it.

Laser distance measurer

I got to play with a laser distance measurer. It fires a pulse of laser light at the wall and times how long it takes to come back. See below for the distance. You can shine it an angle.The light scatters a bit so no matter which angle you shine it, some comes back to the handset.

 It was more fun with a mirror where the scattering didn't work. So the laser light bounced off the mirror up to the ceiling, scattered from that and then back the way it had come, Impressive.

Ada Lovelace and the Konigsberg Bridge problem

The Weston Library had a display about Ada Lovelace. She is regarded as the first computer programmer. She was a friend of Charles Babbage who designer the first calculating machine and she is credited with writing the first algorithm for a machine like that.

I was interested to see the Konigsberg Bridge problem mentioned. I remember hearing about it when I was at school. Essentially it is a question of whether you can cross seven bridges once in a single journey as they were laid out in the town of Konigsberg. https://en.wikipedia.org/wiki/Seven_Bridges_of_K%C3%B6nigsberg You can read about how Leonard Euler proved it was impossible. It brings up the mathematical concept of "graphing" -  ie drawing networks. I have posted about this before when dealing with knots.

Embroidered referencing in the New Bodleian

What was the New Bodleian has been turned into the Weston Library with exhibition space and a cafe.To mark the 800th anniversary of the Magna Carta, someone decided to embroider the whole Wikipedia page on the subject. It's huge. What I love about Wikipedia is the way that it is well-referenced. I have been trying to teach my classes to include (date accessed) when referencing web pages. This is important because unlike printed material, they can change.

Is the reflected light still quantised?

I was going to post about low energy bulbs giving out quantised light rather than a full black body spectrum like a filament bulb. The reason is because high energy electrons are fired through a gas in the bulb. The electrons hit the gas atoms. This provides energy to knock different electrons that are bound within the atoms. The bound electrons jump up energy levels and then de-excite, emitting photons of light but only at the frequencies permitted by the electron level jumps. So you get a spectrum with discrete frequencies. I took this photograph with a diffraction grating to illustrate this point. But looking at it, the coloured part is the light from the lampshade - reflected light. It is from a white surface so it is likely to be the same as the bulb, but might it not tend back towards a full spectrum? Need to think about this.

Stripy clouds over Wigton

 I spotted this stripy sky over Wigton this morning - the sort of cloud formation that made me do a lot thinking in the summer. Then I remembered an experiment from the old Nuffield Physics A Level course. Stick a knife blade high up under the narrow flow from a tap and you get a stripy pattern too.

For the tap, it is a stationary wave. At least that's what the book says. For a stationary wave, an incident wave hits an obstacle and bounces back. The incident and reflected waves interfere. Not quite sure where the wave is originally because it's just a column of water. Anyway, it occurred to me that with the clouds, one moving air mass could be hitting another more stationary air mass to replicate the knife scenario...?

"Bad Greenhouse"

A colleague pointed out this website to me: http://www.ems.psu.edu/~fraser/Bad/BadGreenhouse.html I'm interested in getting to the bottom of this. I was taught (back in the days when the next Ice Age was being predicted so before any idea of a runaway Greenhouse Effect) that a greenhouse works because light from the Sun at short wavelengths can get through the glass. These are absorbed and heat the contents. The contents are now warm but not as warm as the Sun, so they now emit at longer infra-red wavelengths which can't get through the glass. I had heard rumours that there might be problems with this. The linked webpage talks about the glass stopping convection. That's undeniably true. I'm really interested in the idea that the atmosphere radiates electromagnetic waves like a star. I've never heard that said before but it's utterly logical. For any black body (the name given in Physics to a perfect emitter of electromagnetic waves (remember that matt black painted objects cool faster..) Wien's Law applies: wavelength of peak emission intensity x absolute Temperature = a constant. So the colder the object is, the longer the wavelength, from my original teaching. But the idea that this could heat the Earth's surface more than the Sun is new to me and may be worthy of some calculations... Hopefully more to follow.

Looking back in Wigton car park

The inside rear view mirror is a plane mirror. It shouldn't distort the object. Theory says that the virtual image (the picture in the mirror) should be the same distance behind the mirror as the object is in front. In other words, it should show true distances. The driver's door mirror is convex. This gives a wider field of view but the image appears further away.

Starlings in ultra-violet

Here's a Starling on Mrs B's garden feeders. Male and female Starlings look identical to me. So how do they decide who is a girl and who is a boy? It turns out that the female Starlings have patches of ultra-violet on their heads. You need to think of ultra-violet as a different - just one that we can't see. It's counter-intuitive - a colour that you can't even imagine. But Starling eyes can see those frequencies. I wonder what it looks like? When we "see" ultraviolet or infrared, they are done as FALSE COLOUR images. Get it explained properly by watching this awesome programme soon whilst it is still on the iplayer http://www.bbc.co.uk/iplayer/episode/b06pm7t8/colour-the-spectrum-of-science-3-beyond-the-rainbow

Filament light bulbs

I found these clear glass filament bulbs in a tea shop with a retro feel. This is what the first sorts of light bulb looked light. The idea was to put a high enough current through a strip of conducting wire to make it glow without burning. The bulb contains an inert atmosphere so no oxygen can get in to react. If it did, the filament would burn away quite soon. Carbon was the first to be used - remember that graphite conducts. I have no idea whether these are carbon, platinum or tungsten, which was the most commonly used. Too much thermal energy was being produced by this type of bulb for each unit of light produced - but clearly not enough thermal energy to heat your room. It was wasted and so made the bulbs less efficient. This is why they have been replaced by the small fluorescent tubes.

A primitive rain gauge

Mrs B came up with the idea of using a weighted bucket as a primitive rain gauge to measure the weekend's deluge. This is what we made on Friday. The sides of the bucket are almost straight-sided. It would be important for the hole at the top to have the same area as the bottom. I put the cover on to stop leaves and stuff like that blowing in. The rocks are to stop it blowing away in the gales. I lifted them out to measure. It collected 60mm over 12 hours on Saturday night - that's wet. It is very open and could be susceptible to evaporation problems in strong wind and strong sunshine. I should work on a more conventional design.

Trying to estimate the rainfall

It has been raining hard in Cumbria this weekend. They were predicting up to 250mm. That certainly hasn't happened in Wigton but when we drove down to Keswick today it was very wet. I'd estimate that Derwent Water was about a metre up on normal. Here are some pictures:

The lake is fed from the streams that come in from the hills. Any land that feeds a stream going into Derwent Water is its catchment area. From the map, I'd estimate the catchment area as perhaps 14km x 7km making an area of about 100 square km to 1 significant figure. Estimating the lake as 4km x 2km gives it an area of 8 square km. This puts the catchment area as 12 x the lake area. Water in the lake 1m higher would mean a rainfall of 80mm over the catchment. Some of the water would not yet have fallen; some of the water is still flowing down from the hills and some of the water has flowed out towards Bassenthwaite Lake. Even so, 250mm hasn't happened, which is wonderful news. That's what they are saying on the weather bulletins tonight.

Underground cables on the Southern Upland Way

We found a set of underground cable markers on the Southern Upland Way west of Moffat. I went looking for information about how deep they were buried but found this instead http://www.emfs.info/sources/overhead/specific/132-kv/ Click on the "underground" option. I cannot verify this data. Maximum magnetic field strength would be less than 10 microTeslas. The strength of the Earth's magnetic field is between 25 and 65 microTeslas so I don't think the reported reading is significant. I need to take my magnetic field measured if I go again!

Verdünnen Schwerkraft auf meine Physiktasse

Dieses Jahr studiere ich Deutsch. Ich will etwas auf Deutsch schreiben. Ich habe über meine Physiktasse gedacht. Ich sehe, dass die Gewichtskraft zwei Komponenten hat. Eine Komponente ist senkrecht zur Oberfläche. Auf Englisch sagen wir „Normal Reaction Force“. Die andere Komponente heißt die Hangabtriebskraft, die nicht so groß wie die Gewichtskraft ist. Das bedeutet, dass die Beschleunigung des Balls nicht groß ist. Auf Englisch, heißen wir das „dilute gravity“. Die Koordinatenachsen sind senkrecht, aber ich denke wieder über dem Fall, wenn sie nicht senkrecht seien.

Making a loudspeaker

My class made loudspeakers like this. We put alternating current from a signal generator into a coil of wire, which was taped to the back of a paper cone. The coil turns into an electromagnet but with north and south poles that alternate with the current. The coil-electromagnet sits between the poles of a permanent magnet. They alternately attract and repel, which makes the cone vibrate and you get a buzzing noise at the set frequency.

Crooke's Radiometer

I remembered this experiment and it turned out we had it in the cupboard. It's like a 4-paneled weather vane in a partial vacuum. When you shine a light on it, the vane spins. I gave out what I understood to be the explanation, but I was wrong! I said that the momentum of the light photons, calculated by De Broglie's equation, changes on impact with the vanes, so you get an impulse.Thinking about it now, I can see a flaw in my own reasoning. The impulse force would need to create a torque but the light shines equally on both sides as far as I can see. The shiny side would reflect light so there would be a greater change in momentum  and thus a bigger impulse on the shiny side. This would mean it turning anti-clockwise. In fact, it turned clockwise. The real explanation is thermodynamic. I'm still digesting it, but it's here, with a film of it in action https://en.wikipedia.org/wiki/Crookes_radiometer