Late sunrise in the Cotswolds

Sunrise has been getting a little bit later every morning since the solstice although the hours of daylight have been increasing. Things are complicated by the way that the Earth has two cycles of motion. It spins on its axis but at the same time it moves around the Sun. This means that it has to rotate through 361 degrees to get to the point where the Sun is the same height in the sky. Also the Earth follows an elliptical orbit around the Sun. At the moment the Earth is closer to the Sun than at other times of the year (see diagram on http://www.jwstelly.org/TheCalendar/Gregoria nCalendar.html According to http://www.bbc.co.uk/news/magazine-30549149 this means that one rotation of the Earth lasts 24 hours and 30 seconds at the moment. I think I'll need to draw some diagrams to get to the bottom of this. And that's before you chuck in the tilt of the Earth. But the darkest morning will be Jan 2nd and then it gets better.

Hot and cold in Tewkesbury Abbet

 Tewkesbury Abbey is heated by two amazing boilers. Each is surrounded by fins to increase the surface area because they give off infra-red thermal radiation. As such they are painted matt black to be the best emitters.

I also found this max-min thermometer. It's so old that it is marked in Fahrenheit only. It looks like a proper mercury thermometer. It doesn't look to have been reset for a long time. Translated into Celsius, the minimum is about 6 Celsius and the maximum 20 Celsius. That's a bigger range than perhaps I expected. The thermometer is on the opposite side of the nave to the heaters so there must have been a period of sustained hot weather.

Warhol reminds me of quarks

The three versions of the same painting by Warhol in three different colours reminded me that charge for the strong interaction comes in three types. Electromagnetic forces have two types of charge and these are called + and -. But there are three quarks needed to make a baryon and three together would add up to zero. The idea for colour charge came from the way that red, green and blue add up to make white in the primary colour definition. So the three quarks in a baryon would be assigned red, green and blue charges to make that baryon colourless.

Warhol: high contrast

I found this painting in the Andy Warhol exhibition at the Whitworth Gallery in Manchester. I have been teaching about contrast media used in medical physics. X-rays are attenuated by high density materials, dependent on atomic number. Calcium is especially good at attenuating X-rays so bones block X-rays but soft tissue containing water, mainly hydrogen and oxygen, mostly let X-rays through. There is a big contrast between the two media and you get a clear image of the bones. X-rays of organ systems like the digestive system fare less well because the muscles attenuate as badly as the contents. So patients are given a barium meal which occupies the space inside the bowels which attenuates a lot so giving high contrast with the muscle walls, The barium meal is called  a contrast medium.

Series circuit in Manchester

I liked these Christmas lights in Manchester. Traditionally, tree lights were wired in series so that there was only one way round the circuit for the current to flow. Hence if one bulb blew, it turned off the current so that all bulbs went out. Then you spent Christmas testing every bulb individually to find out which one had actually blown. These must surely be wired in parallel!

Measuring the remains of the balloon

Last month I did some calculations based on my birthday balloon. http://wigtonphysics.blogspot.co.uk/2016/11/finishing-birthday-balloon-calculations.html The balloon has now been laid to rest and I took some measurements. I was wrong about the mass of the balloon. At 10.34 grams it is less than half of my estimate. Also the thickness turned out to be twice my estimate and exactly what the Internet told me it should be. So  my estimate of dimensions must have been wrong!

Great Slab on Bowfell: ancient caldera lake

Great Slab on Bowfell was one of my great days out this year. I had been thinking about a post about coordinates on an inclined plane. But then I found out why it is so flat: volcanic ash settling in water in an ancient caldera lake. This time last year I was in a modern caldera. And the evidence as to why it was a freshwater lake is given on http://www.ronaldturnbull.co.uk/pics/geopix/Pages/17.html

Sounding the horn

I liked this little horn - it looks like the ones they had on the very first cars. The horn is a tube that has a stationary wave inside it. Assuming that this works like a trumpet, it will act as a closed-end pipe which will have an anti-node at the blown end and a node at the open end. The pressure difference as the sound hits the room pressure will cause some reflection of the wave back down the tube. As the reflected wave crosses the incident wave, interference happens to create a stationary wave. The length of the tube is one quarter of a wavelength for a closed-end pipe so in this case the wavelength will be about 60cm. The frequency will be 550 Hz which is well within the human hearing range. The bell at the end of a trumpet is about accommodating different resonances but here it may well just be to make the sound directional.

Callibration problems

These thermometers were all supposed to be showing the same temperature. How would we know which one is correct? There is a range of almost 2oC. Each one might be correct to the nearest 0.1oC but I'd suggest that an uncertainty of +/- 1oC might be more appropriate based on what are effectively repeat readings. We'd need to put them in melting ice and into boiling water to check them properly.

Cyclic time in How (Not) To Be Secular

This book is a work of theology, philosophy and sociological observation. It is a commentary on the book The Secular Age by Charles Taylor. It explores the idea that scientific logic is not the only way that humans choose to view the world. In classical physics I am used to the idea that time is a linear process that just runs on irrespective of the material world. Relativity put paid to that idea and quantum physics suggests that time is grainy and doesn't even flow smoothly. Following Taylor, James Smith notes that "There are two ways that we shape time, and thereby give shape to our world: cycles and narratives.  ...cycles of time make the world for us and thus delineate significance.... We also "gather" time in narrative and story. We organise our own identities in an implicit (or sometimes explicit) autobiographical narrative." This is not a physics way of dealing with time but as the yearly cycle of the Sun begins again on the solstice, it might be fitting to note the way that the passing of the seasons can give significance to our lives. Feeling maybe, not objective, but a powerful emotion none-the-less.

The Mountains of the Moon

As part of my learning of lunar features, I've been trying to identify some of the high points from the photographs I've taken. The features were named by European astronomers in the last few hundred years, hence them being named after European mountain ranges. There is a problem with measuring the heights because there is no sea level as a base for measurements on the Moon. A particular distance from the centre of the Moon has been used for this.

Water is a product of combustion

When it was very cold last month, there was clear evidence of water being a product of combustion behind this car. It seems strange to students who can't see water when things are burning, the temperature being too high for liquid water and the H2O being in the form of water vapour. But the cold ground behind the exhaust caused the water vapour to condense onto the dry stones.

Physik im Advent: ice cube problem

I finally found out that they are doing Physik im Advent this year. Here it is https://www.physik-im-advent.de/ You can change it to English in the top left hand corner. A bit of a spoiler, but I had to try today's, day 18. Place a match stick onto an ice cube and pour salt over it. After a couple of minutes I was able to pick one of the ice cubes up. The match stick had stuck to it. It's likely that the trick depends on the ice cubes being below and not at 0 Celsius. Adding salt means that it will turn from solid to liquid at say -2oC. But if the salt does not reach the ice under the match it will stay solid at that temperature. As the ice turns to water, the temperature remains constant, presumably at -2oC. This would refreeze any surface melt below the match and stick it to the ice cube.

Thinking about fog on the Solway

This started with an observation. We drove out of sunshine in Kirkbride and into mist at Bowness-on-Solway. Then we headed along to Campfield Marsh and came back out of the mist. Looking back, there was mist over the water but not over the tidal sands. Bowness is where the channel comes close to land and would thus get the conditions that exist over water. I'm guessing that the humidity must be higher over the water. The air above the water shouldn't be colder than over land. The temperature of the sea does not vary very much because it has such a big thermal mass. In fact, sources suggest that the air over the sea should be warmer than over land on a clear night. http://www.metlink.org/other-weather/science-in-the-sky/fog/ The suggestion is that cold air from land moves out over the sea and puts the water vapour below the dew point. I'm guessing that what I saw must be due more to humidity than temperature.

My deflated birthday balloon

After two months my birthday balloon is sinking. These balloons are made of aluminium rather than rubber because the gaps between molecules in rubber, whilst small enough to stop air molecules escaping easily, are big enough for the tiny monatomic helium to get through. The gaps in aluminium are smaller but the helium escapes gradually. I was expecting that there would come a point that the weight would be bigger than the upthrust and the balloon would sink to the ground. Upthrust is equal to the weight of air displaced and that depends on the density of the air. This suggests that the density of air in the room is not uniform and is lower nearer the ceiling. So there is a density gradient. I suppose it's a bit like the Galileo thermometers.

Rutherford's Garden

Ernest Rutherford's world changing discovery of the nucleus happened in Manchester and this garden outside the museum in Manchester references that. I was struggling to work out what the message is though.

SPDT switch or AND gate: security light wiring

I inspected our security light and found that it had two live wire connections: the red wire on the right and one of the two brown wires on the left. In fact this wire has a brown sleeve over a yellow wire. The cable in is 4-core not 3. It took me a long time to figure it out. It's wired like a landing light combination. The motion sensor on the light fixing is one switch but there is an override switch below that just turns the light on regardless. Here's a wiring diagram for stair lights:

The switches are called Single Pole Double Throw SPDT switches. Double throw because they can make the bulb come on whether up or down but depending on the state of the other switch. For the security light, the two wires between the switches are the 2 live wires. Then there are neutral and Earth wires making 4-core. I don't think the switching is quite identical to the landing light switch because the override switch turns the light on regardless of the sensor. But when the override switch is thrown the other way, the light only comes on when the sensor switches. That mode has two switches in series so acts as an AND gate. Both override switch AND sensor have to be on to make the bulb come on.

Controversial candle and bell jar experiment

 I hadn't done this experiment for years since I became aware of a problem with the old standard explanation but I was looking for a demonstration to promote discussion of combustion. I lit a small candle and had it float on a petri dish in a trough of water. I took the bung out of the top of a bell jar and lowered it over the lit candle. Taking the bung out allows air to be displaced from the bell jar. The bottom of the bell jar was propped on masses in a few places to allow circulation of water underneath. Then I put in the bung. After a while the candle went out and the water level on the inside of the bell jar rose.

The old standard explanation was that the candle used up the oxygen and that water flowed in to take its place. On a good day, the water rise is nearly 20%. These days I don't understand why I never questioned it. Yes, combustion does use up oxygen but it also makes carbon dioxide and water vapour. The water vapour condenses as the experiment cools and a little carbon dioxide dissolves in the water which might produce a small reduction in volume. The main reason for the reduction in volume is due to cooling after the flame goes out. The problem is that the flame had to be lit before the bell jar was placed and sealed so that the air inside it was hot already. After the flame goes out, the gas cools and contracts and that is the main reason that the water level rises. The give away is that the main rise in water level happens when the flame has already gone out.

The other issue is that only a little of the oxygen is used up before the concentration becomes too low for combustion. See http://misconceptions.science-book.net/wp-content/uploads/2011/09/Chap2-1.pdf for the full details.

Impact breccias and asteroids

I was interested to find this in a museum in Manchester. I had come across breccias before as being rock shattered when a fault forms and then hot mineral rich water flows into the joins. The water evaporates and the mineral cements the fragments. The classic sign of this is when the bits have sharp corners so no rounding has been caused by transport. It had never occurred to me that a big meteorite or asteroid strike could do the same. So how do you tell the two types of breccia apart? Is it in a known impact crater? Impact can produce so much heat that the minerals can turn to glass which might be observed. Is there too much iridium isotope that has to have come from outer space?

Energy flow for a bow and arrow

 This exhibit in the museum at Manchester University gave me an opportunity to practise the energy stores language. The display even calls it "stored energy". So pulling the bow, I'd say that the chemical energy store in the human goes down and via the pathway of mechanical work the elastic energy store in the bow goes up a lot whilst the thermal energy store in the surroundings goes up a bit. Then the arrow is fired so the elastic store in the bow goes down and via the pathway of mechanical work the kinetic store in the arrow goes up a lot whilst the thermal store in the surroundings goes up a bit.

Gatesgarth: cold on the valley floor

I felt the cold coming down Scarth Gap when we reached the top of the trees on the way down. Then I noticed that the smoke from the farm was rising only to spread horizontally 20 metres up: evidence of a cloud inversion. The smoke is less dense that the air around it because it has been heated and has expanded to become less dense than the air around it. Hence it floats upwards. As it rises it willcool a bit. There must be a layer of warmer, less dense air above 20 metres. The smoke is no longer less dense so it can't rise. It's quite low for this to happen, I had been hoping for a proper cloud inversion but the humidity levels can't have been right even though there was a temperature inversion. Temperatures are supposed to go down as you go up in the atmosphere. The shadow of the fells is so deep in winter that sunlight cannot reach the valley floor to warm the lowest layer of air during the day. There was no wind to disturb the layers of air.

Belt of Venus and backscattering

Now I know what to look for, I see the Belt of Venus all the time. Here it is this morning. It's the pink glow above the horizon. I was looking north. The darker line below is the shadow of the Earth. The Sun has not yet risen and we are technically still in shadow. It is light because the Sun is lighting the atmosphere above our heads. This morning it occurred to me that when I show red sky at the lab, it is as a result of scattering. The shorter wavelengths are scattered out of the way so the blues and greens are knocked out of line and only the red longer wavelengths get through. But this is a transmission phenomenon. In the picture, the red light has gone past us. So how can I see it? Turns out that it is called BACKSCATTERING. https://en.wikipedia.org/wiki/Backscatter It seems to be a type of reflection, but one that doesn't reflect all rays in the same direction as a mirror would.

A Cumbrian in Manchester

We visited the Christmas markets in Manchester and found a famous Cumbrian. John Dalton from Cockermouth moved to Manchester in the early 1790s. He is most famous for giving us the theory of atoms in chemical elements that we still use today. But I like it that he was one of the first people to measure the heights of the Lakeland fells using a barometer. He must have been a very early fell walker.

Atlas on Haystacks: inertia and gravitational mass

Pretending to be Atlas holding the world with this erratic boulder on Haystacks reminds me of the problem with two different types of mass. Gravity is pulling down on the boulder so it has weight W=mg. If we tried to push the rock with resultant force F the acceleration would be calculated with F=ma. The equations have the same form. In the second equation, which goes with Newton's Second Law, mass in kg is called INERTIA. It is resistance to change in motion. Now imagine we let the boulder fall, the resultant force would be the weight so we'd get W=ma. Isn't this the same as the gravitational equation? So is g the same as acceleration due to gravity? Here's the problem with the two ways of thinking about mass. For gravitational mass, g is 9.81 N/kg - the gravitational field strength. If we let the mass fall, the acceleration due to gravity will be 9.81 m/s2. Why is this the same size as gravitational field strength? No one quite knows. It is called the equivalence principle. Some experimenters are working to stupid numbers of decimal places to try to measure a difference between the two masses. But maybe they really are the same.

Latent heat of fusion for ice to water

 The specific latent heat of fusion is the number of Joules of energy needed to turn 1kg of ice into water at a constant temperature. We used an electric heater in a glass funnel of ice so that only the melted water is weighed.

 A problem was that the heater melted a tube around it and the rest of the ice had fused so that it would not fall into the hole created. So the heater was tending to heat the air. This will mean that more heat than expected will be needed to melt 1kg. Our value will be too high.

 The electrical method allows the heat energy input to be calculated by ItV. The data is set out below.

The true value for water is 3.34 x 10^5 J/kg so it's not too bad. As explained, the value is higher than it should be. Another reason for this value being too high is that we had to heat the ice from say -5 Celsius to 0 Celsius before it started to melt.

Imploding drinks can

 We put about 1 cm of water into the bottom of an empty drink can. Well, it wasn't really empty; it was full of air. We boiled the water strongly so that steam was coming out of the can for nearly a minute. This drove the air out of the can and now we had a can full of steam. Then we quickly flipped the can upside down into the bowl with one smooth movement. It was important to land the opening of the can into the water. The water quickly cooled the steam down so that it condensed. In the liquid state the particles took up less space so now most of the inside of the can really was empty. It was a partial vacuum inside. The can collapsed inwards with a bang.

A can is normally fine because air particles on the inside pushing outwards are balanced by air particles on the outside pushing inwards. With a partial vacuum the air particles outside have nothing to balance their inward push. The can implodes.

Blue snow holes near Great Gable

 I stopped to look at the view and noticed that the post hole in the snow looked quite like it had blue light about 10cm down. I found this explanation  http://www.webexhibits.org/causesofcolor/5C.html  Some light penetrates the snow surface and travels downwards. It is scattered or absorbed by the ice crystals. Red and yellow are best absorbed. You can find a graph of it here http://www.webexhibits.org/causesofcolor/5B.html The blue is scattered and bounced around. That's what you see.

BBC Bitesize Revision for GCSE

Here's where you find Biology 1, Chemistry 1 and Biology 1
http://www.bbc.co.uk/schools/gcsebitesize/science/aqa/

Here's where you find Biology 2, Chemistry 2 and Physics 2
http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/

Electrolysis of a molten salt

I worked in a fume cupboard to attempt the electrolysis of molten lead bromide. This photograph was taken through the glass window. It started out as a white powder and took a long time to melt. You can see that there is an orange gas in the beaker. This shows that bromine gas has been produced. It is a toxic gas - hence the fume cupboard. Bromide is a negative ion so is attracted to the anode. The lead is a positive ion and so is attracted to the cathode. The lead was hot when the electrodes were extracted from the beaker and soon turned from grey to yellow. I'm guessing that in the heat it had oxidised and the yellow was lead oxide. When it was all safe, I photographed the end:

The cathode was the right hand one. Perhaps that's a rim of lead.

Keswick flood defences and a centripetal force

I was interested that the flood defences were not an equal height all the way along. Surely the water will flow over the lowest bit... The answer is that the higher bit is on the bend. The water has inertia and would rather keep going in a straight line at constant speed. The bank has to push on the water to stop it going straight and push it round the bend. This force is a centripetal force. That's OK for the water that is actually touching the bank but water molecules aren't actually joined. Away from the edges there is little to stop the water layers sliding over each other and heading towards the edge. This means that at the bend the water level will be deeper on the outside than on the inside. Water is very hard to compress so there will be some form of rigidity lower down but the shear forces between layers to stop sliding will be weak.