MORE than 80 people attended the April Open meeting of Crediton’s U3A group which included a talk given by Professor Roy Sambles called “The Wonder of Light”.

Roy had a raised platform so that he could be seen while demonstrating with a multitude of equipment. He shared with us why he thought he became interested in Physics and he thinks it’s his name, Roy, which is the beginning of ROYGBIV - the colours of the rainbow!

The room was darkened and the scene was set for a scientific adventure…but the lights had to be switched on so we could actually see the professor while he was speaking!

The professor then showed us that placing two polaroid sheets at 90 degrees to each other will stop light. Then adding strips of sellotape (other sticky tape is widely available and works just as well) set at 45 degrees to each other between the polaroid sheets will let different colours appear. Roy explained that we would be able to say why this happened by the end of the talk.

Roy used a length of red science rubber tubing to demonstrate the different wave forms and wavelengths - I’m sure we all remember this tubing from the bunsen burners in our science lessons at school.

It was explained that light is emitted as electrons in atoms drop levels and give out energy in the form of light. The Sun acts a a huge nuclear reactor and the energy formed is emitted as light which is necessary for life on Earth.

We learnt how Newton was very scientifically astute as in the 1660’s he discovered by experimenting with candlelight and calcite crystals that light behaves as a wave but also must be made of particles. Roy demonstrated this experiment to us using an overhead projector instead of a candle.

Roy showed us how passing an electrical current through a filament will cause it to glow and eventually to burn out as the Oxygen in the air enables it to catch fire. This caused a mini fire behind Roy that was pointed out by an audience member and extinguished. If the Oxygen is removed from the glass bulb the filament will last forever so manufacturers don’t produce a total vacuum in the bulb as they would never make any profit.

Roy used a smoke machine to demonstrate how a laser beam is refracted (bent) as it passes through water and how the angle of refraction changed as milk was added to the water. The use of another medium e.g water, glass, diamond etc changes the speed of the light and causes it to bend.

Several philosophical questions were also posed to the audience.

By the end of the highly entertaining and fascinating talk the questions about the sticky tape demonstration were answered - it’s to do with the long chains of parallel molecules in the tape.

Professor Sambles then went on to answer questions from the audience. Many thanks to Roy for a thoroughly “illuminating” talk delivered on the audience’s “wavelength”. I wish you had been my A level Physics tutor - I would definitely have got a better grade!

The next Open Meeting will be held tomorrow, Wednesday, May 15, and will include a talk by Felicity Goodall entitled “Devon’s conscientious objectors”.

The June 19 meeting will see Bryan Short give a brief history of coinage.

For more information please visit the website: U3asites.org.uk/crediton or telephone David Agasee (chair) on 01363 775698.

Jo Poulton