The Electromagnetic Spectrum
We have already learnt that light is a type of wave. It is one of the waves of the electromagnetic spectrum. We call it visible light because it can be seen with our naked eyes.
In the topic light you would have used different shaped glass blocks to make the light rays change direction. If you use a prism you can split white light into the different colours of a rainbow or of the spectrum.
Different colours have different frequencies. Red has the lowest frequency and Violet has the highest frequency.
Remember frequency is the number of waves past a point.
Just outside the range of visible light on the violet side is Ultraviolet.
Just outside the range of visible light on the red side is Infrared.
William Herschel (1738-1822) discovered Infrared radiation in 1800
Herschel passed sunlight through a prism. As sunlight passes through the prism, the prism divides it into a rainbow of colours called a spectrum Herschel was interested in measuring the amount of heat in each colour.
To do this he used thermometers with blackened bulbs and measured the temperature of the different colors of the spectrum. He noticed that the temperature increased from the blue to the red part of the spectrum. Then he placed a thermometer just past the red part of the
spectrum in a region where there was no visible light and found that the temperature there was even higher. Herschel realized that there must be another type of light which we cannot see in this region. This light is now called INFRARED
What to do next...
STILE (Online)
Printable
More Information?
