## total internal reflection

Earlier this week, we used semi-circular perspex blocks to investigate total internal reflection.

I’ve put together a short video showing total internal reflection in a semicircular block and a perspex model of an optical fibre.

There are some nice ray diagrams explaining total internal reflection on BBC Bitesize.

Cyberphysics has some examples of how optical fibers are used and the youtube video below shows how they can be used by doctors to see inside a patient’s body.

## Nat5 waves & radiation exam 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!

## half-life calculations

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.

## the geiger-muller tube

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.

## electricity and energy revision questions

Here are questions from Standard Grade and Intermediate 2 that are appropriate revision for the electricity and energy unit of national 5.  Answers to follow.

## dynamics & space revision questions

Here are the revision questions for dynamics and space.  They are taken from old standard grade and intermedite 2 past papers.  I have adjusted the marks to fit national 5.

## nat5 revision

Use the attached file to help with revision for your test on Monday.  Start at the beginning of the booklet and read up to the end of page 41.

Thanks to Mr Noble for sharing his notes. 🙂