2.4 - Collecting volcanic ash

This week we set about collecting some of the volcanic ash from the recent Grimsvotn eruption. We collected this data as part of a British Geological Survey project to track the spread and concentration of the ash cloud.

We used sellotape and old catalogues atop a Land Rover in the car park; leaving these out for the entire school day on Tuesday. Thereafter, we attached the tape to the back of a sheet of paper which we will send to the British Geological survey for analysis.

Hopefully we'll have picked up some ash throughout the day. Pretty amazing when you think that it has travelled around 1000 miles to get to where we are.

How to make a webcam into an infrared camera

Every time I teach about infrared radiation, I have a lot of nice images I can show my classes and maybe even a clip or two from 'The Predator' to go with them. I saw an email today offering an infrared camera as part of your attendance on a course and it reminded me of the fact that I have always wanted one to show realtime images in the infrared spectrum.

Given that I've got a little more time on my hands than I normally do, on account of it being the exam season, I set about trying to make myself one.

I opened up the nearest webcam and screwed off the plastic section surrounding the lens. On the back of it and found the infrared filter.











I duly removed it and replaced the infrared filter and set about replacing it with a visible light one. I initially cut a small square from some blackened x-ray film and tested it but I was still seeing some colour. This guide  suggested that the best visible light filter could be scavenged from the negatives of some old colour film.


This was the trickiest part of the process but I eventually managed to fit two small pieces of this film in place on the back of the lens.


I've tested it briefly and it looks pretty good. I'll post some images later.

My camera was a basic Creative Live Cam but other manufacturers should be constructed in a similar fashion. A nice cheap alternative for bringing infrared into the classroom!

5CH - Past papers by topic

Now uploaded for the whole course. All of you should be working through these over the holiday, picking out the topics you find most difficult in the first instance. Any problems, give me a shout.

5CH - MOSFETs

Look at the last device which uses p-type and n-type materials to conduct - the MOSFET. It will only switch on if there is a sufficient voltage across the gate of the transistor.

5CH - P-n junctions

By putting some n-type and p-type materials together you can make all sorts of wonderful devices. Diodes, LED's, solar cells and LDR's all rely upon the technology of semiconductors. We explained how each of these devices work in terms of electrons and holes. You need to be able to distinguish between reverse bias and forward bias as well as photovoltaic mode and photoconductive mode.

5CH - Semiconductors

Started semiconductors today. Semiconductors are, as the name suggests, materials that 'sort of' conduct electricity. We can add impurities to an element - the process is called doping - which allows the electrons to move. This can be done by adding an element with an extra electron (n-type) or by adding an element with one less electron (p-type).

5CH - The Bohr model of the atom

Did more work on the Bohr model today. Energy is taken in by the electron to jump up one level or more and energy is given out in the form of a photon as the electron moves back down to its original level. The energy required to move from one level to the next can be displayed in an energy diagram. The bigger the gap between the lines, the more energy it takes to move between the levels. These energies are always shown as negative with the ionisation level (where the electron leaves the atom) being at 0 Joules.