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Most classes have done some work recently on improving answers to the kind of questions that ask you to describe/explain/justify. I haven’t saved all of the mindmaps that have been produced but this one is fairly typical of the responses generated by a class. There is a pdf version available to download.
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We have almost completed the health physics unit and have spent some time in class practising half-life problems. You might find the attached instructions helpful as you prepare for the unit test.
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I have attached your HW on health physics. It covers material from before the holidays so you may want to look over your jotter notes to help complete the questions.
Please hand in your HW no later than Tuesday 7th September. Late jotters will not be accepted.
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Here is your HW for next Tuesday (7th). Remember that late jotters will not be accepted.
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We examined the operation of a Geiger-Müller counter today.
image by Theresa Knott
The Geiger-Müller (GM) counter is used to detect ionising radiation such as alpha and beta particles or gamma rays. The radiation enters through a very thin window at one end of the tube. This window is usually made of mica.
Mica flakes. Photo by Rpervinking
Mica is a mineral that forms in layers called sheets. These sheets can be split apart into very thin layers, so thin that even an alpha particle can pass through it (remember that alpha particles can be stopped by something as thin as your skin or a sheet of paper). The mica window prevents the argon inside the tube from escaping and also stops air from getting into the tube.
When radiation enters the tube and collides with an argon atom, an electron may be knocked off the atom -- we call this process ionisation. When ionisation occurs, a positively-charged argon ion and a negatively-charged electron are produced. The argon ion is attracted to the outside wall of the tube, which is connected to the negative terminal of the power supply, while the electron is attracted to the central electrode, which is kept at a high positive voltage -- typically 500V.
A small pulse of current is produced each time an electron reaches the central electrode. These pulses can be counted by an electronic circuit and a displayed on a 7-segment display. Sometimes a small speaker is added to the system to produce a click for each pulse. On its own, the GM tube cannot tell the difference between alpha, beta and gamma radiation. We need to place different materials (e.g. paper, aluminium, lead) in front of the mica window to discover which type of radiation is responsible for the reading.
Here is a short video demonstrating the use of a Geiger-Müller tube.
The thunderstorm this morning reminded me that I was going to post something about calculating the distance to a storm.
Play this video and then replay it, paying close attention to the time index at the bottom. You will need to move your cursor over the video box to keep the time visible.
Lightning from Daniel Dingemanse on Vimeo.
Can you calculate the distance between the flash of lightning and the camera?
Hint: take the speed of sound in air as 340 m/s.
The Physics experts at Sixty Symbols have been playing with a vuvuzela. Here is a film showing their experiments on frequency and sound filtering.
This powerpoint file from the High School of Glasgow summarises the function of different electronic components and explains their use in common voltage divider circuits. There is a pdf version of the file below.
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This amazing footage of the Saturn V rocket launch for the Apollo11 moon landing mission has been put online by Mark Gray. The video provides an extra dimension to the launch photograph in my earlier post about Newton’s 3rd law of motion. While that picture shows an enormous plume of gas being forced out of each rocket exhaust, the video below demonstrates the heat of the gases and the effect they have on the structure of the launch pad itself.
Apollo 11 Saturn V Launch (HD) Camera E-8 from Mark Gray on Vimeo.
I found a great set of summary notes provided by the Physics Department at James Gillespie’s High School in Edinburgh. They cover the entire course, so are quite long. The diagrams are very clear and I would recommend working your way through them as part of your preparation for the May exams.
The notes are in a pdf file so they will work with iTunes or you can download them by clicking on the link below.
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