Here are the answers to the waves & radiation questions.
I’ve put together a collection of exam questions from old standard grade and intermediate 2 papers that fit the national 5 curriculum. Try these before moving on to past papers and check your answers using the solutions that I will post next. No cheating!
I’ve attached a short guide to half-life calculations. There are some questions after each worked example, answers are at the end of the sheet.
We’ve examined the operation of a Geiger-Müller counter as part of the radiation topic.
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.
Here are whole unit summary notes to help you prepare for the unit test next week.
Thanks to Mr Noble for sharing his notes.
Here are some revision notes on waves to help you prepare for the unit 3 test next week.
The unit assessment for the Waves & Radiation unit of National 5 is scheduled for next week. These notes will be useful as you prepare for the test.
Thanks to Mr Noble for sharing these notes.
X-rays are a form of electromagnetic radiation. They have a much higher frequency than visible light or ultraviolet. The diagram below, taken from Wikipedia, shows where x-rays sit in the electromagnetic spectrum.
image by Materialscientist
Wilhelm Röntgen discovered x-rays and the image below is the first x-ray image ever taken. It shows Mrs. Röntgen’s hand and wedding ring. The x-ray source used by Röntgen was quite weak, so his wife had to hold her hand still for about 15 minutes to expose the film. Can you imagine waiting that long nowadays?
This was the first time anyone had seen inside a human body without cutting it open. Poor Mrs. Röntgen was so alarmed by the sight of the image made by her husband that she cried out “I have seen my death!” Or, since she was in Germany, it might have been
that she actually said.
Röntgen continued to work on x-rays until he was able to produce better images. The x-ray below was taken about a year after the first x-ray and you can see the improvements in quality.
Notice that these early x-rays are the opposite of what we would expect to see today. They show dark bones on a lighter background while we are used to seeing white bones on a dark background, such as the x-ray shown below. The difference is due to the processing the film has received after being exposed to x-rays.
In hospitals, x-rays expose a film which is then developed and viewed with bright light. X-rays are able to travel through soft body tissue and the film behind receives a large exposure. The x-rays darken the film. More dense structures such as bone, metal fillings in teeth, artificial hip/knee joints, etc. block the path of x-rays and prevent them from reaching the film. Unexposed regions of the film remain light in colour.
Röntgen’s x-ray films would have involved additional processing steps. The exposed films were developed and used to create a positive. In creating a positive, light areas become dark and dark areas become light. So the light and dark areas in Röntgen’s x-rays are the opposite of what we see today. Our modern method makes it easier to detect issues in the bones as they are the lighter areas.
Röntgen was awarded the first ever Nobel Prize for Physics in 1901 for his pioneering work in this field of physics.
I have attached a recording of a short BBC radio programme about the first x-ray and what people in the Victorian era thought of these new images. Click on the player at the end of this post or listen to it in iTunes.
Earlier this week, we looked at the electromagnetic spectrum, including ultraviolet radiation.
image courtesy of sonrisaelectrica
The section of the electromagnetic spectrum with wavelengths ranging from 10nm to 400nm is called ultraviolet radiation (uv for short). Sunlight contains uv rays and it’s those uv rays that are responsible for the suntan you get during the summer holidays. This Australian animation shows how the ultraviolet in sunlight causes our skin to tan and explains why too much uv will damage our skin. The SunSmart page has loads of information on staying safe in the sun.
The damage that uv can do to cells is put to good use in some sterilisation equipment, such as this bottle for safe drinking water and the toothbrush sanitiser shown below.
The Nobel Prize for Medicine was awarded to Niels Rydberg Finsen in 1903 for his research into the effects of ultraviolet on the bacteria that cause tuberculosis.
British banknotes have security features built into them. These features are only visible under uv. This image of a Clydesdale Bank £10 note shows part of the pattern that can only be seen under uv light.
image from Science Photo Library
There is a Bank of England leaflet (pdf) with further information on the security features in our banknotes.
Remember that whenever something glows under a uv light, we’re not seeing the uv radiation itself because our eyes can’t detect ultraviolet. Instead, we see the fluoresence; visible light given out in response to the uv falling on the material.
Some hair gels fluoresce under uv light. Here is someone with some of the uv gel in his hair.
but we don’t see anything until we turn on the uv light.
You can even buy genetically modified tropical fish that glow under uv light.
Here are solutions to the Waves & Radiation exam questions. I have added a breakdown of the marks in red.