microwaves & infrared

• what wavelength and frequency do microwaves and infrared waves have?


  long wavelengths and low frequencies because they're on the left of the EM spectrum
• what are the two groups of microwaves

  • the ones that aren't absorbed by water molecules
  • the ones that are absorbed by water molecules
• how are microwaves that aren't absorbed by water molecules used for satellites?

  • communication using satellites.
  • because the satellites are so far away from earth the microwaves have to pass through the earths atmosphere
  • they wouldn't be able to do this if they were absorbed by water molecules, this is because our atmosphere contains a lot of water
  • once the microwaves make it through they are received by a satellite and transmitted back down to earth where we can detect them using a satellite dish
  • with this we get things like satellite tv
• how are microwaves that are absorbed by water used for microwave ovens?

  • to heat up our food
  • because most of the food we eat contain water molecules, when light waves are fired at our food the energy from those waves gets absorbed by all the water molecules
  • as the water molecules start to vibrate more with all the new energy they transfer some of the energy to neighbouring molecules
  • this is so it spreads throughout the food via conduction and convection
  • this is why foods that contain more water tend to heat up quicker in the microwave
• what is infrared radiation (IR) emitted from?

  all objects that have thermal energy. the amount they get emitted depending on the temperature.
• the ______ the object the more infrared radiation it will emit

  hotter
• how is infrared radiation used for spotting living organisms?

  • infrared cameras that help us see in the dark, in particular to help us spot living organisms
  • by using a special camera that can detect IR we can see which areas are hot and which areas are cold by measuring how much IR they emit
  • animals that are very warm will appear quire bright because they emit lots of IR
  • whereas their surroundings which are much cooler will appear dark because they don't emit as much IR
• how is infrared radiation used for cooking?

  • by heating metal to very high temperatures, like in ovens and grills, we can make the metal emit lots of IR
  • this can then heat our food by transferring the heat energy, causing it to cook
  • unlike it microwaves, IR doesn't penetrate the surface of the food, this is why bread toasts in a toaster instead of just getting warmer
• how is infrared radiation used for electric heaters?

  • these devices use electrical energy to heat up the metal of the heater
  • then because its so hot it emits IR to the surroundings, this is how it's able to heat up our rooms
• are microwaves and infrared waves harmful to us?

  only in high quantities (e.g. putting your hand in a toaster)