One of our own members, Alan Kenwright, stood in at short notice at the July meeting and spoke on “What use is a Rainbow”, an intriguing title. He began on familiar ground by describing what happens to white light when it passes through a triangle of glass and produces a spectrum of different colours (different wavelengths). He then introduced us to the term “spectroscopy” which is the study of how substances interact with light (more accurately called electromagnetic radiation). Spectroscopy allows the identification and study of substances quickly and accurately without at the same time destroying them and this has become extremely important analytical tool in modern scientific methods.
Our eyes can detect visible light which is only a small part of the electromagnetic spectrum. Many other animals can detect much more. Sophisticated machines have been developed to detect and analyse light or radiation and its interaction with other substances. An enormous number of uses have been found for electromagnetic radiation and Alan described
some of these.
Infrared light is a type of electromagnetic radiation with wavelengths longer than visible red light. We can’t see it but can often feel it as heat. Ultra violet light which causes sunburn is also electromagnetic radiation with wavelengths shorter than visible light. Shining infrared and ultraviolet light on certain substances can make them appear different colours which can be useful e.g., in detecting forged bank notes, checking driving licences, postage stamps and envelopes. X-rays have very short wavelengths and can pass through many materials making them useful in medical imaging and security screening. X-ray fluorescence can be used to identify elements present in materials without damaging them. Gamma rays have the shortest
wavelength and can be used in radiotherapy, equipment sterilisation and food preservation. NMR and MRI scans, which many in the audience will be familiar with, use gamma rays to produce detailed images of internal organs and tissues.
This was a brilliant talk from Alan, who made a complex topic accessible to a mixed audience and showed that light (the rainbow) or electromagnetic radiation has lots of beneficial uses.