- Electro-magnetic Spectrum
- The electromagnetic spectrum is a continuous range of wavelengths. The types of radiation that occur in different parts of the spectrum have different uses and dangers - depending on their wavelength and frequency.
- All of these waves travel at the same speed in free space, which is the speed of light or about 300,000,000 m/s (metres per second).
- White light can be split up to form a spectrum using a prism. This 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. This is called dispersion.
- 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:
- infra-red radiation is felt as heat and causes skin to burn
- X-rays damage cells causing mutations (which may lead to cancer) and cell death - this is why doctors and dentists stand behind protective screens when taking lots of X-rays
- gamma rays also damage cells causing mutations and cell death
- Ultraviolet radiation - UV - is found naturally in sunlight. We cannot see or feel ultraviolet radiation, but our skin responds to UV exposure by turning darker over time. This is called a sun tan. 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 cells to become cancerous.We should wear UV blocking sunscreen on sunny days to avoid skin cancer. Overexposure of our eyes to ultraviolet radiation can cause blindness, so we should wear hats and sunglasses on sunny da