Inside a Geiger-Muller tube

 

Here is a view into one of our Geiger-Muller tubes. Note the cylindrical central anode. The window is made of a mineral called mica which has a low mass per unit area and thus allows alpha to pass relatively uninterrupted. There is low pressure gas inside - perhaps 1/10th of atmospheric pressure. When one radioactive detection occurs, it starts with the ionisation of one gas atom to make an ion-electron pair. The electrons are pulled towards the central anode, being accelerated as they go. They gain so much energy that they are able to ionise more atoms to create more electrons and so on. This electron avalanche effect produces enough to be detected.

Newton's First Law and the linear air track

 

I wanted to tell my youngest class that forces do 3 things: they change shapes of objects and change direction and speed of movement. I decided to use the linear air track for the latter two. The air track removes the friction so the glider travels at constant speed between the ends. The action of forces on the elastic bands changes the direction. I could have added that that the shape of the elastic changes. They don't know yet about hysteresis loops in the elastic but this dissipative process means that after each impact the speed visibly decreases. In between impacts, Newton's First Law applies.

What are wind turbine blades made of?

 

I had always assumed that the blades were made of low density metal like aeroplane wings. Turns out they are made of carbon fibre and are thus not recyclable. The Guardian ran an article about 5 years ago about the problems of recycling carbon fibre. See also https://www.latimes.com/business/story/2020-02-06/wind-turbine-blades

A weird dream about the thermometer

 I had a dream about the mis-calibrated thermometer. In it, I took the battery out and it worked again so I had a go.

I'm glad I did because I found some interesting stuff inside. The display is powered from the metal contacts at the top of the green board through the bendy piece that looks like a licorice all-sort - the pink thing with the black middle. It is flexible and slightly compressible so it makes good contact and I'm assuming that the black middle must be a conductor. When I put it all back together, itm was working correctly again - but a day later it went back to its old ways! Oh well...

Platinum Jubilee Hassock reminds me of Hofmann Voltameter

 

Mrs B made a Platinum Jubilee Hassock which was blessed today - an awful lot of work went into it! I knew platinum was ringing some bells - it is the platinum  electrodes. And I have used these in the Hofmann Voltameter. Platinum is used because it is so unreactive that it doesn't interfere with the reactions.

A badly calibrated thermometer

 

One of my students pointed out that this thermometer is reading below zero at normal room temperature. It is about 20 degrees Celsius too low. It has occurred to me that I would need to check it over a range of temperatures to see if the error remains the same each time so that there is a true systematic error. 

Something strange about the Watchtree turbine

 

Having said that the Watchree Vestas were 660kW, I noticed that the sticker on the new display turbine mechanism claims 1300kW and that it dates from November 2017. Questions to look into are 1. How long do the working parts of a wind turbine generator last? 2. Were the turbines upgraded or do you always fit a turbine with a higher spec on its name plate?