3.12 explain some of the uses of electromagnetic radiations, including:

radio waves: broadcasting and communications

  • Long wavelengths (10km)
  • Long wave radios (1-10km) can be transmitted from London to any country because long wavelengths are best at diffracting
  • They can bend around the earth, around hills and tunnels

 

  • Short wavelengths (10-100m)
  • Shot radio wavelengths can be received at long distances from the transmitter because they are reflected from the earth’s ionosphere (electrically charged layer in the Earth’s upper atmosphere)

microwaves: cooking and satellite transmissions

  • Relatively short wavelengths – 1cm-10cm
  • Used in satellite communication.
  • Needs to use wavelengths of microwaves that can easily pass through the Earth’s atmosphere without needing to be absorbed
  • For a satellite TV to work, signal from the transmitter is transmitted into space where it is picked up by the satellite receiver that is orbiting around the earth
  • Satellite transmits the signal back into earth in a different direction where it is received by a satellite dish on the ground

 

  • Microwaves in ovens – different microwaves penetrate a few cm into the food before being absorbed by the water molecules in the food

infrared: heaters and night vision equipment

  • Aka heat radiation given out by anything and everything (the hotter the object, the more frequently infra red waves are being emitted)
  • Examples would be electrical heaters that radiate infrared to keep us warm and night vision goggles sensing the heat given off by other organisms

visible light: optical fibres and photography

  • Visible light is used in communication by optical fibres carrying data over long distances as light pulses
  • Optical fibres work by bouncing waves off a very narrow core
  1. Beam of light enters fibre at a certain angle as one end is continually reflected (internal reflection)
  2. This happens until the light ray emerges. This is used in telephone, broadband internet cables and MRI scans 0a429977de9f911975ab91491b4fbe65ee868876.gif
  • Cameras use lenses to focus visible light onto light sensitive film or electronic sensor (aka aperture function controlling light intake)
  • Shutter speed determines how long the film/sensor is exposed to light and by varying the aperture, you can decide to capture very little or a lot of light

ultraviolet: fluorescent lamps

  • Fluorescent lights/colors look vibrant because ultraviolet radiation (UV) is absorbed and visible light is admitted
  • UV light is safe to use as all radiation is absorbed by the phosphorus coating on the inside of the bulb and is ironically more efficient than regular light bulbs

x-rays: observing the internal structure of objects and materials and medical applications

To produce an x-rayed image :

  1. X-ray radiation is directed through your body
  2. Onto a detector plate
  3. X-raus can see through less dense mediums such as flesh but not through dense mediums such as bone hence making them so useful for examining bone injuries

gamma rays: sterilising food and medical equipment

  • Medical equipment is sterilized by gamma rays to kill microbes
  • Food is sterilized in the same way as gamma rays are less harmful as they are not radio active
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