Moseley and X-ray spectroscopy part 2

 The apparatus consisted of a rack of pure samples of elements inside a vacuum tube above.

 When that element was in the centre of the tube, it came under a cathode that fired a beam of electrons down onto it, shown above.

To avoid having to break the vacuum every time a new element was tested, there was an ingenious pulley system where turning a knob at the top turned a cotton reel which moved the line to which the rack of elements was attached.

The beam of X-rays from the sample then went into this chamber where it hit a prism made of a salt. The beam was then deflected round the chamber and the results photographed at different angles recorded on a scale inside.

Moseley and X-ray spectroscopy part 1

I found a wonderful display about the physicist Henry Moseley in the History of Science Museum in Oxford. I'd not heard of him. He made important progress on elements and the Periodic Table using X-rays. The idea is that electrons are fired at an element with such high energy that they are able to dislodge electrons from the inner electron energy level. When they fall back to the level, they emit X-rays. The spectrum of such X-rays must be unique to each element in the same way as the spectrum of light from an excited gas vapour lamp is when I do this in class.

Lower Borrowdale Volcanics: a landscape of low viscosity

Reading Paul Gannon's book I found that the initial volcanoes in the Lake District produced lava with a lower silica content. This meant that the lava had a lower viscosity and was able to flow more freely. The result was a lower landscape of tiered lava flows and rocky knolls. This central Lakeland landscape is shown above and tends to catch the water, becoming peaty. These earlier volcanic rocks are called the Lower Borrowdale Volcanics. I was interested in why the silica content affects the viscosity and this link explains it really well http://sci.sdsu.edu/how_volcanoes_work/Controls.html  I am interested to see that SO4 radicals can polymerise by covalently bonding together. These polymers increase the friction in the lava. The next site gives reasons why you might go from having low silica content to high silica content due to tectonic drift over millions of years. Nearer a plate boundary there will be a higher silica content.  https://www.geolsoc.org.uk/ks3/gsl/education/resources/rockcycle/page3655.html

Coanda Plate on Hayewater Gll Hydro

I went to examine the water intake on the gill by Hayeswater. The odd thing is that although water pours equally onto the top of the weir and through the by-pass, no water is visibly coming off the bottom of the weir. I went to inspect. It is made of thin wire and the water passes through into the hydro-electric pipe. It is said to work by the Coanda Effect. On a convex surface, the fluid tends to stick to the surface. I wondered why it needed to be such a fancy idea rather than just a wire filter. I suppose that debris will not be pulled to the surface and will carry on in accordance with Newton's Laws of Motion. Perhaps debris would have sat over and blocked the grill of a conventional filter.
https://elginseparationsolutions.com/coanda-screens/

Equations on the window: restaurant in Oxford

At one point Physics students were writing equations on the window of the refectory and now the habit seems to have been picked up by one of the restaurants in town. A perfunctory glance suggests that they look OK. There are only two given in the form that we teach in school. lambda = Ln2/T gives a value for the decay constant in terms on the half-life. Ek = 1/2 mv^2 is the standard equation for kinetic energy.

Ploughing boulder on Gray Crag

I posted 3 years ago about ploughing boulders https://wigtonphysics.blogspot.com/2016/09/ploughing-boulder-on-whit-fell.html We came across this perfect example high on the slope of Gray Crag above Hayeswater on the route up from the old dam. Its furrow is several metres long so if it really does move at a few metres a year then this has been on the move for several centuries. Further to what I said about the frequency of freezing events on a fell near the Irish Sea, this boulder is on the east facing slope 30 miles from the sea on hills that are said to be the last in the Lake District to have retained glaciers in the Ice Age (as per the Paul Gannon book). So this hillside should see more freezing. It is also very steep so perhaps it moves further every year. The earth piled up in front of it is particularly impressive.

Geese flying in formation

I've known for years that geese fly in a V formation to save energy but what exactly is going on? They are not hidden behind the one in front like the cyclists who are having the air flow blocked. It turns out that the upwash from the wingtip of the one in front provides some extra lift - in other words they don't have to beat their wings as strongly in order to support their weight https://en.wikipedia.org/wiki/V_formation Upwash and induced drag are technical terms new to me and will need further study.

Avoirdupois

This year's Mothers' Union diary has a word that I've never come across. I though that pounds and ounces were the Imperial system. It appears that there is a much older system called Avoirdupois which was then adopted into law in Britain in the 1800s. I was interested to read that the pound was divided into 16 ounces because 16 divides evenly by 2 several times. I suppose the systems were devised by merchants originally and are based on practical considerations rather than mathematical logic. Try https://en.wikipedia.org/wiki/Avoirdupois_system and https://en.wikipedia.org/wiki/Imperial_units

Orange light in Stonethwaite

Only last week I was showing my class a sodium vapour lamp and saying that there were no longer lamps like that anymore. They still exist at the end of Borrowdale. Yellow light is a mixture of  red and green, so let's approximate for orange. According to the theory, red objects should reflect the red in the light but absorb the green so they should still look red. However, a blue object would absorb both red and green, thus appearing black. This is what the text books say but I am never convinced.

The sound of the rain by Derwent Water

Mrs B made an interesting observation on a very wet Duke of Edinburgh checkpoint by Derwent Water. Out in the open when the rain hits the umbrella, you get a higher frequency sound than when you stand under the trees. I suspect that the drips from the trees are bigger drops, so does that mean that with umbrella fabric you get a deeper note if you hit it harder? I can't believe that this is true for a drum, but further thinking is needed.

Volcaniclastic sediment on Bowfell

Following Paul Gannon's book, we went to see the volcaniclastic sediments on Bowfell on the way up from Three Tarns. These layers are the back on the Great Slab, which is the top sloping layer of these sediments. These layers are apparently formed from dust and ash from volcanoes that settled in the bottom of lakes in the large Scafell Caldera. He talks about volcaniclastic sandstone so I went to see the thick darker band. It is made of lumps a bit like large barnacles. He also says that some layers were disturbed by earth tremors before they had fully solidified and so have swirled patterns. I found these

4 probe method for resistance

It turns out that the regular method that I use for measuring resistance is called the 4 probe method. In this experiment I am running current through a wire and measuring the voltage. As I change the length of wire, I adjust the potentiometer to keep the current the same. I measure the voltage each time and divide by the current to get the resistance. I was taught the method many years ago by a wide older colleague who said that the constant current keeps the temperature of the wire constant and eliminates it as a variable. This must be true. But in the 4 probe method, the current is kept constant to eliminate the effect of contact resistance. In the 2 probe method, the voltage is kept constant whilst the current is varied. The current flows through the contacts and there must be a potential difference across the contacts which means that the voltage recorded will not be the true value. As the current changes, that potential difference will also change since p.d.=IR. In this 4 probe method, no current flows through the voltmeter if it has sufficiently large resistance so there is no contact resistance p.d. and the voltage recorded is true.

Bad Step Tuffs

I have finally found a book that is helping me to make sense of the Scafell Caldera. Cumbria Libraries have multiple copies. I found it first as a Google Book with this search https://books.google.co.uk/books?id=cjwfT_nDvLQC&pg=PA53&lpg=PA53&dq=paul+gannon+scafell+caldera&source=bl&ots=TShZ0eZEtr&sig=ACfU3U1jaN3oIxGGNNFVKZ0JfiYXTx_VrA&hl=en&sa=X&ved=2ahUKEwj0iYLaoIjlAhVhoFwKHVRYDkcQ6AEwAnoECAkQAQ#v=onepage&q=paul%20gannon%20scafell%20caldera&f=false
He has sorted out for me the Borrowdale Volcanics. Apparently there were two phases - the Lower Borrowdale Volcanic Group and the Upper BVG. Lower was lava and Upper was explosive. Upper was the time of the Scafell Caldera. The explosive erruptions produced a lot of dust and ash which fell to earth, settling in lagoons in the caldera and becoming sedimentary rock. It began to make sense of this document http://nora.nerc.ac.uk/id/eprint/3234/1/RR01007.pdf . As we were going up Crinkle Crags, I decide to look out for the tuffs listed on page 21 of Geological Survey document. Here's the approach to the Bad Step

 I picked up the rock below in the vicinity. It is certainly weathered pink but whether it is really a Bad Step tuff as opposed to any of the other identified Crinkle ones I'm not qualified to say. There must have been a lot of individual eruptions in the area.

Odd shadows

 The shadows above perplexed me, appearing to give me a halo. Then it occurred to me that what seemed like a halogen spotlight in the ceiling above was probably an LED replacement version, Sure enough, by using my fingers in a strobing pattern, I was able to see 3 white LEDs. The photo I took below somehow comes up with a ghosted image of them. The dark part of the shadow must be where my head was blocking out light from all 3 LEDs. The halo will be shadow caused by just 1.

Raindrop lenses on Helm Crag

The lensing effect of these raindrops on Soft Rush is impressive. We must be further away than the Principal Focus because the image is inverted. The white bottom of the drop is actually the sky. The image is smaller or diminished which means we are beyond twice the focal length. Another time I need to try to measure the focal length. Here's what was being focused, on a moody day above Grasmere

Two terminal method for resistance

I had thought that an ohmmeter was an example of the two probe method for measuring resistance but it seems that a modern meter is probably actually a disguised 4 probe method. https://en.wikipedia.org/wiki/Ohmmeter I know that on old meters, you had to zero it every time before you started. The old meters were really just recalibrated ammeters and worked on the principle that a bigger resistance produced a smaller current. It seems that these modern ohmmeters put a constant current through and measure the voltage. A problem with this method of measuring resistance is the resistance of the leads (as shown below) and the unknown problem of contact resistance.