How far is it to the sky?

Mrs B found this lovely book for me. It contains this page

Which begs the question: how far away is the sky? This led me to find out about the Karman line https://en.wikipedia.org/wiki/K%C3%A1rm%C3%A1n_line Karman calculated the altitude at which an aircraft would not be able to travel fast enough to generate enough lift to support itself without travelling faster than the orbital speed for that altitude. So this is where the sky is said to end and space begins. It's arbitrary but I like that it is based on a calculation.
There was a new moon tonight just visible through the trees.

So

Midsummer Chronophage in Cambridge

This weird clock and another similar are star attractions in Cambridge. It took me a long time to work out how to read them. The outermost light races round in a second. I took repeat shots that show that the shutter is not always open for the same amount of time. One complete lap lasts a minute. The inner lights show that the time was roughly 20 to 5.

Another mathematical bridge

I have been past this bridge at Iffley Lock many times but hadn't realised that it is a replica of the Mathematical Bridge in Cambridge. The angled or horizontal long sections are tangents to the circular arc of the bridge. The almost vertical short posts are radii.

Knitted mathematics in Cambridge

Being someone who knits, I was amazed to find in the Whipple Museum of the History of Science these mathematical surface models knitted by a scientist over a century ago. There is more about them here: http://www.sites.hps.cam.ac.uk/whipple/explore/models/knittedinterpenetratingsurfaces/ It reminded me of when I was trying to make a model of a Riemann surface out of paper five years ago. http://wigtonphysics.blogspot.com/2015/01/trying-to-make-riemann-surface.html

Mathematical Bridge in Cambridge

I'd heard about this and also heard that there were myths about it, but now I understand it, I'm really impressed. The diagonal timbers are all tangents to the circular arc of the bridge and the upright posts are radii of the greater circle. https://en.wikipedia.org/wiki/Mathematical_Bridge I'm now on the hunt to find the replica near Oxford.

Josephson Junction

I also found this at the Cavendish Laboratories. I'd heard of Josephson Junctions but had never bothered to look it up. It turns out to be quantum tunnelling with superconductors, so that it is Cooper pairs of electrons that tunnel through the barrier. https://en.wikipedia.org/wiki/Josephson_effect

JJ Thomson and the electron

I was very pleased to visit the site of the old Cavendish Laboratories in Cambridge. It prompted me to look up JJ Thomson. https://en.wikipedia.org/wiki/J._J._Thomson He was experimenting with cathode rays. Following the chain back, it seems that the line of research started with the passing of big voltages through gases - an old-fashioned streetlight, in other words. Then they started to improve vacuums until they could remove all of the gas. They realised that they had a straight line ray. This is where Thomson came in. He was able to bend the rays with magnets and electric fields, to work out the charge-to-mass ratio. He realised that the particles were negative and smaller than an atom. The world of sub-atomic particles was born. I'm amazed by the number of Nobel laureates that he taught, including Wigton's own William Henry Bragg.

An interesting fact

This is a birthday card that I received. I think it is an ironic take on the spurious correlations that get noticed. My favourite is the one that says that the more ice creams that are sold, the more people drown. There is no causal link. The ice creams don't cause the drowning but are consumed on hot days when more people go wild swimming. On this card, there is clearly a causal link but it is trivial.

Light in the sea

I was interested in this display at Maryport Aquarium. If the top 200m makes up 25% of the oceans, then the oceans cannot be as uniformly deep as I'd imagined. The detail on the absorption of  different light colours is exceptional. I recently found out that ABSORBANCE = log10(intensity in/intensity out). If only 20% of light has reached 10 metres, the absorbance = (1/0.2) = 0.70.

Life cycle analysis

I have had to teach Life Cycle Analysis in recent years. This is a tool to calculate the impact of a particular product based on the energy and environmental damage involved in raw materials, manufacture, transport and disposal. I was surprised by one that I saw that put polystyrene cups ahead of waxed paper cups. The latter are lighter and so less fuel is used in transport. The balance on that one might have shifted now that waxed paper cups might be becoming more recyclable. In the case of the paper towels, they need raw materials and are heavy to transport. The wet paper won't be recycled. So this is another example of where a paper product might seem to be a better option than using electricity, but masking the fact that more electricity and fossil fuels were used in manufacture and transport. I think people prefer paper towels because they seem to give drier hands faster.

More electrolysis with the head torch

To clean the copper sulfate from the copper contacts in the head torch, I put that part of the case in dilute hydrochloric acid overnight. Somehow it seems to have acted as an electrolytic cell. The top contact seems to have been cleaned and has a layer of new copper. The other contacts have been cleaned to some extent but now have a layer of what is presumably copper chloride. There was no battery connection so there should have been no potential difference between the contacts. I'm surprised at what has happened because there was no difference in metal like there was on the human electrolyte cell I found at Green's Mill two weeks ago. Anyway, the acid has done the trick and the head torch is working again.

Problems with Charles' Law

We are fortunate to have a set of apparatus for performing the Charles' Law experiment. The problem is trying to get the concentrated sulfuric acid plugs into the capillary tube. Concentrated sulfuric acid is sued because it absorbs water vapour from the air column making sure that it is just dry air pressure being measured. We dry the empty tubes in the oven before up-ending them into the acid. The idea is that the air then cools and contracts, pulling the acid down the tube. It doesn't go down far enough so that the air column is covered by the water bath. It doesn't seem to affect the results but is still not very satisfying.

Copper sulfate corrosion in a head torch

I was amazed to find blue copper sulfate crystals in the battery compartment of this head torch. To be fair, the alkali cells were 5 years beyond their label date. The contacts are copper, but where did the sulfate ions come from? The were 2 AA alkaline cells in the compartment. The electrolyte is thus potassium hydroxide. Mrs B is suggesting that it might be from the plastic in the case. Rubber is vulcanised by using sulfur to provide cross-links. Sulfur trioxide will react with potassium hydroxide to make sulfate ions.

I should have timed the oscillation

The second non-barbed wire down on this fence at Dinorwig Quarry skips the next pole and thus spans 5 metres between nodes. That would give a 10 metre wavelength when oscillating as a stationary wave. It made a note that was inaudible. I should have timed the oscillation to get the frequency. Next time, with frequency and wavelength, I'll be able to calculate the wave speed. I can estimate the mass per unit length and thus get the tension. I need to find another fence!

Physik im Advent

Heute ist der erste Adventstag. Jedes Jahr gibt es einen Physikkalender mit vielen Experimenten. Es hat begonnen. Man kann es hier finden. https://www.physics-in-advent.org/ Man kann Deutsch oder Englisch waehlen.