IGCSE Physics / The electromagnetic spectrum
Uses of visible light, ultraviolet, x-rays and gamma rays
Edexcel International GCSE Physics (4PH1), chapter 11: The electromagnetic spectrum, specification point 3.12. Free lesson.
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Visible light, ultraviolet, X-rays and gamma rays are useful because each interacts with materials in a different way. These differences allow them to carry information, produce light, show the inside of the body and kill bacteria.
How visible light and ultraviolet are used
Visible light travels along optical fibres, which are thin glass threads. Doctors use these in endoscopes to see inside the body. Cameras detect visible light from objects, which is how photography works. Ultraviolet (UV) is invisible, but some materials absorb it and then give out visible light. Fluorescent lamps use UV absorbed by a coating inside the glass. The coating gives out visible light. Security marks use special ink that is invisible in ordinary light but glows under UV. This can help identify marked valuables.
How a fluorescent lamp makes visible light
A fluorescent lamp works in two stages. The gas gives out UV, then a coating changes that energy into visible light. The UV itself cannot light the room because it is invisible.
How X-rays show a broken bone
X-rays pass through soft materials, such as skin and muscle, but are absorbed by denser materials such as bone and metal. A detector records how many X-rays pass through each part of the body, creating an image. Most X-rays pass through soft tissue and reach the detector. Bone absorbs X-rays, so fewer reach the detector behind it. The bone appears pale. At a break, X-rays pass through the gap, making a dark line in the image.
How gamma rays sterilise
Gamma rays kill bacteria, so they are used to sterilise food and medical equipment. Sterilising means making something free of germs. Gamma rays can pass through packaging, which means sealed equipment can be sterilised without opening the packet. Gamma rays kill bacteria on the equipment or in the food. They pass through plastic packaging, so the equipment stays sealed during sterilisation. Sterilising food with gamma rays does not make the food radioactive. The rays kill bacteria but do not make the food give out radiation.