radiomicrowave infrared visible ultraviolet X-raygamma ray Long wavelength Low frequency Short wavelength High frequency The first X-ray of human bones. Wilhelm Conrad Roentgen discovered X-rays serendipitously whilst experimenting with vacuum tubes. He took this image of his wife’s hand a week later. Clearly visible are the bones of the hand and her ring. The X-rays pass easily through soft tissue but cannot penetrate bones and teeth so these show up as shadows in the image. X-rays are now routinely used in medical applications as a diagnostic probe. Image courtesy NASA/GSFC A boy in the infrared. Objects between about 70K to 1000K emit a substantial fraction of their total output in the infrared. Infrared imaging is used to locate people trapped in collapsed buildings and by police to track suspects at night. Infrared radiation is also used in the remote control that operates your television. In the image below the hottest regions are in white and yellow and the coolest in purple and blue. Image courtesy NASA/IPAC Fibre optics. Optical fibres, made of drawn glass, have revolutionised communications. Much cheaper than copper cables, fibres are able to carry far more data. They are also lightweight and flexible, so allow access to confined spaces; useful in medical imaging. Ultraviolet security marking. Phosphor-loaded inks glow when exposed to ultraviolet radiation, yet remain invisible under optical wavelength light. The inks are commonly used to verify the authenticity of banknotes and tickets. Ultraviolet lights are also used to check for forged paintings. Modern paint contains phosphors whereas older paints do not, thus UV light can be used to differentiate between old masterpieces and modern imitations. Microwave cooking. Microwaves heat food by exciting the water molecules within it. Regions of constructive and destructive interference are set up by waves reflected off the oven walls and so a turntable is used to rotate the food to ensure that it is evenly cooked. Microwaves are also used in communication systems such as mobile phones. Galileo satellite network. Radio waves are used in global and satellite communications (television and radio signals). The Galileo system will combine signals from several satellites to allow the user to determine their location on Earth to within a few metres. The Gamma Knife. Living cells are very sensitive to gamma radiation. By exposing patients to small doses of gamma radiation doctors can reduce the size or even remove cancerous tumours. The gamma knife uses dozens of narrow beams of radiation. each beam too weak to cause much damage but when added together they are very powerful. In this way tumours within the human brain can be precisely targeted. Image courtesy Elekta instruments Image courtesy Adam Hart Davis/DHD Multimedia Gallery Image Courtesy ESA Image Courtesy HowStuffWorks.com >10 -1 m m10 -3 m10 -4 m10 -7 m10 -8 m m m< m10 -5 m m m m The Electromagnetic Spectrum: Applications