What is a spectrum?
The visible spectrum a rainbow appears to come out of the prism
Using a prism, you can split up white light to form a spectrum. (A prism is a block of glass with a triangular cross-section.) The light waves are refracted as they enter and leave the prism. The shorter the wavelength of the light, the more it is refracted. As a result, red light is refracted the least and violet light is refracted the most, causing the coloured light to spread out to form a spectrum.
The electromagnetic spectrum
Visible light is just one type of electromagnetic radiation: there are various types of electromagnetic radiation with longer wavelengths of light than red light and with shorter wavelengths than violet light. All the different types of electromagnetic waves travel at the same speed through space.
The discovery of infrared
National Maritime Museum London UK
British astronomer William Herschel (1738-1822) was making observations of the sun when he put coloured filters over his telescope in order to make his observations safer. He noticed that different coloured filters heated up his telescope by different amounts. Using a prism to break up visible light he put a thermometer in the different colours. He found that the temperature rose as he moved the thermometer from violet to red. He then measured the temperature where there was no visible light, at the red end of the spectrum. The temperature was the highest: he had discovered infrared.
The discovery of ultraviolet
Following Herschel’s work, Johann Ritter (1776-1810) tried to find invisible rays at the violet end of the spectrum. As part of the experiment he used silver chloride, which turns black when exposed to light. This happened fastest when exposed to the invisible rays at the violet end of the spectrum.
The main types of electromagnetic radiation
X-rays, visible light and radio waves are all types of electromagnetic radiation.
The main types of electromagnetic radiation frequency type of electromagnetic radiation wavelength highest gamma radiation shortest X-rays
lowest radio waves longest All types of electromagnetic radiation: are transverse waves travel at the same speed in a vacuum - empty space.
The speed of electromagnetic radiation in a vacuum is 299,792,458 m/s. This is approximately three hundred million metres per second - nearly nine hundred thousand times faster than sound, which is why you see a flash of lightning before you hear the thunder.
Hazards of electromagnetic radiation
Over-exposure to certain types of electromagnetic radiation can be harmful. The higher the frequency of the radiation, the more damage it is likely to cause to the body: microwaves cause internal heating of body tissues infrared radiation is felt as heat and causes skin burns
X-rays damage cells, causing mutations (which may lead to cancer) and cell death gamma rays also damage cells, causing mutations (which may lead to cancer) and cell death.
Microwave radiation can be used to transmit signals such as those for mobile phone calls. Microwave transmitters and receivers on buildings and masts communicate with the mobile phones in their range.
Ultraviolet radiation - UV - is found naturally in sunlight. We cannot see or feel ultraviolet radiation, but our skin responds to it by turning darker. This happens as our bodies attempt to reduce the amount of ultraviolet radiation reaching deeper skin tissues. Darker skins absorb more ultraviolet light, so less ultraviolet radiation reaches the deeper tissues. This is important, because ultraviolet radiation can cause normal cells to become cancerous.
The three main types of ultraviolet radiation, and some of