Colorimeter scales and precision

 

The colorimeter absorbance scales come with two different sensitivities. These are given as 0 - 1 and 0 - 2. 1 and 2 would be called the Full Scale Deflection (FSD) because that is the reading when the needle is deflected to the furthest end of the scale. It's easy on the 0 - 2 scale because the numbers are written onto the scale at the bottom.

So the picture above onto the 0 - 2 setting would be 1.83. Absorbance is a logarithm of a ratio so has no units. The scale divisions are 0.05 apart so the way of giving the resolution as half a scale division means we say 1.83 +- 0.025. I'd say by inspection that we can do better than +-0.025. Surely by stating it as 1.83 I really mean +-0.01. 

There are two ways of dealing with the 0 - 1 scale. I have relabeled the scale to show how. I like the top green numbers best. I'm going to say the reading is 0.92 +- 0.01 using the half scale division resolution. But that's the same resolution I was claiming for the top scale. So maybe it's really 0.92 +- 0.005. 

Ergs at the gym

 

I was interested to see this ski trainer at the gym. I knew that ergs are a unit for energy but I hadn't realised what a tiny amount it is. An erg is 10^-7 Joules - and I have always thought that Joules were a disproportionately small amount. I had an idea ergs were American but they were proposed by a European and fit into a metric system. I need to do more work on the C.G.S. system of units.

Absorbance calculations to prove why a colorimeter needs a colour filter

 

I set up a way of thinking about the colour filter. The arrow on the left is the white light made of red, green and blue. Shone at a cuvette full of copper sulfate, let's say half of the red and half of the green is absorbed so the other half is transmitted. The blue light is unaffected so any blue that goes into the cuvette must come out. Io is the abbreviation for the intensity of the light going in and I is the abbreviation for the light coming out. So in my way of doing things, the total going in is 3 and the total coming out is 2.

Now let's insert an orange filter that absorbs all of the blue light.

Then let's apply the formula for the absorbance which is based on logarithms.

Notice that the absorbance value is much higher with the filter in place because the transmitted blue light has been removed. That's why we need a filter in a colorimeter.

Why do colorimeters have colour filters?

 

It has finally occurred to me why a colorimeter has colour filters. Last year I was using copper sulfate solution of different concentrations. A colorimeter shines light through a sample of it placed in a cuvette. It measures the intensity of the light going in and the intensity of the light coming out having been transmitted through the sample. The intensity of the light coming out will be less than the intensity going in because some of the light will have been absorbed. Copper sulfate is blue. That means it absorbs the other colours but all blue light goes through it. Blue is transmitted; it cannot be absorbed by copper sulfate. If we shine white light through, it contains blue as part of its spectrum. That blue light goes straight through. But suppose we use a filter before the sample cuvette that absorbs all of the blue light before it reaches the cuvette. Only the other colours will reach the cuvette and they stand a chance of being absorbed. This time the intensity coming out will be lower. The bigger the difference between intensity in and intensity out, the higher the absorbance. Using the correct filter increases the absorbance.

Brockram in the Cockpit stone circle on Moor Divock?

Brockram is an amazing stone I've seen in the Vale of Eden. Carboniferous limestone from when we were in a coral sea was then eroded when we were in a desert as far north as the Sahara. The stones were not transported far in wadis so they are large and angular and were set into sandstone. Such an amazing story that you can follow down the valley. This stone in a stone circle on Moor Divock between Pooley Bridge and Askham seems almost certain to be brockram, probably getting up there by glacial transport over a few miles.

Magnetic fish tank cleaner

I was interested to see a strong magnet stuck to the glass of this fish tank. It attracts another piece through the glass which can then be dragged up and down the glass to clean it. The glass was about 5mm thick. I can't find any information on the strength of these commercial magnets nor anything about how field strength decreases with distance for pole-faced magnets. For a current-carrying conductor, it it is double the radial distance, halve the field strength. I think I'd need to do some experiments with this to find out the thickness of glass at which it no longer attracts.

Back to rippled stratus

The sky was amazing this morning. The same widely ribbed stratus stretching from Skiddaw to Cross Fell that I blogged about last month. It is definitely higher than Cross Fell at about 900m because I could see the summit but there is cloud above it. I guess it is stratus because stratus is between 1000m and 2000m. A bit of research suggests it is probably the type referred to as Stratus undulatus. Then at right angles in the layer above, seen through the gaps in the undulatus, there was an alto- version of it. That suggests that the winds at that much higher altitude were at 90 degrees to the lower winds.

Refraction by an angel

 

I noticed this rainbow spectrum appearing on the door frame and traced its origin to a glass angel hanging in the window.

Looks like its the chiseled edge at the bottom which is acting as a prism. Just one side was causing the refraction. The sun went in before it was possible to see if the other side could work at the same time.

Camber Castle and Weald Sandstone

 

Here was me thinking that I'd come to chalk country in Sussex and Kent. This display board at the marvellous Camber Castle alerted me to the idea that the Weald is largely sandstone - admittedly laid down in the Carboniferous period. I have looked up Fairlight near Hastings on BGS GeoIndex and it gives that sandstone as being part of the Wadhurst Clay Formation. The stones weathered nicely.

Entropy: the myth of Sisyphus and Rye Harbour

 

At Rye Harbour, the elements move shingle along from the Hastings end eastwards every year. Every winter, it is dug out, loaded into lorries and taken back to the Hastings end! It seemed to me a good example of the way energy has to be expended to maintain a system in higher entropy or greater order than would be natural. In order for that to happen, the total entropy or total disorder has to be increased elsewhere. This will be from the wasted heat energy from the machinery. It reminded me of the myth of Sisyphus.

Planetary conjunction

 

I'm pretty slow on the uptake with some ideas. Whilst we were in Kent, I was sure that Venus and Jupiter had swapped places overnight. Turns out they had. Thinking about it, they are on the same plane as seen from Earth but Venus is moving faster across the sky, so at some point it will catch up and pass Jupiter, as seen from Earth. So at some point, they must occupy the same point in the sky. From deep in my memory, I dredged up the phrase "planetary conjunction". Turns out it is the correct term. And there was a conjunction of Venus and Mars in the early morning, 12 hours before I took this photo. See here.

The sensitivity of a mercury barometer

 

This barometer was on the wall at Lamb House in Rye where Henry James used to live. The top section got me thinking about how much the mercury would be expected to rise or fall due to normal changes in atmospheric pressure. Using the formula for pressure at the bottom of a fluid = height x density x g, with atmospheric pressure given as 101325Pa and density of mercury as 13546kg/m^3, you get a height of 762mm. This is said to be 1013.25mBar so 1mm is worth 1.33mBar or 1mBar is worth 0.75mm. Say a low pressure was 980mBar, then the mercury would need to go down by about 25mm. It looks like the display at the top has the capacity to go up and down by that amount.

Electromagnet in the escape room

 

Well we did escape from Leicester in the end. In the escape room, you have to solve clues to find number codes to enter into terminals. If you get it right, a box pops open with more clues. Turns out the doors are held shut by electromagnets so entering the correct code must turn the current off. The is a compression spring which must have a weaker force than the electromagnet which then provides the resultant force to push the door open.

Betelgeuse dimming doesn't mean it's about to explode

 

The star Betelgeuse, which is one shoulder of Orion, is a red supergiant and very bright. I have always been told that it could go supernova at any time. Now 4 years ago, it started dimming and people were wondering. The July 2022 edition of Physics World contains a nice explanation based on the realisation that a Japanese weather satellite always has it in view. So they were able to go through images back to 2017 and concluded that part of the star surface had cooled and had stopped warming a gas cloud close by, which then condensed into obscuring dust. Shame! It would be a great spectacle to see it go supernova.

Belt of Venus

 There has been a great run of Belt of Venus conditions this winter. The Belt is the pink glow that sits on top of a band of what looks like dark cloud above the horizon. The dark bit is actually the shadow cast by the Earth when the Sun is still below the horizon.

This website explains the pink Belt of Venus very well. I also found out that it isn't named after the planet Venus. It is named from the Greek goddess Aphrodite. 

Embleton Diorite

 

In Alan Smith's book "Lakeland Rocks" page 120 he mentions a quarry that turned out to be huge. He says that the rock was mistakenly called "Embleton Granite" but is really a diorite. Yes, it has the larger crystals that show that it cooled more slowly being underground, compared to the lavas that cool quickly in the open air. But its chemical composition is the same as andesite, an intermediate rock between the basic basalt lavas and the rhyolites. There is a lot of plagioclase feldspar in it - feldspar with more calcium in it - and so not pink like the potassium-rich orthoclase feldspars. There were gold crystals in some samples which we think must be iron pyrites.

Watch Hill Felsite

 

On page 109 of Alan Smith's "Lakeland Rocks", he gives details of a rhyolitic-composition intrusion. I was really impressed by the columns. I hadn't thought there was anything like it in the Lake District. The old quarry is now very well defended by gorse, bracken and brambles!

Zeta Ursa Major

I have never got used to the Greek letters that are used to denote the stars in a constellation. The Plough labels from Alpha at the top of this picture and the circled star is therefore Zeta. However, it isn't actually one star. Looking through binoculars, it is actually two. It is not a binary because they are some distance apart but on the same line of sight. The brightest star is called Mizar and is magnitude 2, which means it is pretty bright to the naked eye. It turns out Mizar is more complicated than it looks. Mizar itself was the first to be found to be a binary system when telescopes were invented. That is two stars orbiting each other. Then later each of those two stars was found to be a binary, so what looks to my eye to be one star is actually four! Now I can pick out a fainter second star next to Mizar. That is not linked to the system and is called Alcor. Alcor itself is a binary as well. So there are 6 stars when it looks like one! See here.