more uses of EM waves

• optical fibres are thin glass or plastic fibres that can carry data over long distances as pulses of visible light. they work because of reflection. The light rays are bounced back and forth until they reach the end of the fibre
• visible light is used in optical fibres. light is not easily absorbed or scattered as it travels along a fibre
• fluorescence is a property of certain chemicals where ultra violet radiation is absorbed and then visible light is emitted. that's why fluorescent colours look so bright - they actually emit light
• fluorescent lights generate UV radiation, which is absorbed and re-emitted as visible light by a layer of a compound called a phosphor on the inside of the bulb. they are energy efficient so they are good to use when light is need for long periods
• security pens can be used to mark property with your name. Under UV light the ink will glow, but its invincible overwise.
• ultraviolent radiation is produced by the sun and exposure to it is what gives people suntan. when it is not sunny, some people go to tanning salons where UV lamps are used to give an artificial suntan. exposure to UV radiation can be dangerous . fluorescent light emits very little UV- safe
• x rays pass through flesh but not through denser material like bone. the radiation that is absorbed or not gives an x ray image.
• radiographers use x rays and gamma rays to treat people with cancer (radiotherapy). because high doses of these rays kill living cells, directed towards cancer cells
• gamma rays used as medical tracer. gamma emitting source injected, progress is followed around body, gamma radiation is well suited to this because it can pass out through the body to be detected.
• both x rays and gamma rays can be harmful to people, radiographers wear lead aprons and stand behind a lead screen or leave the room to keep exposure to them minimum