P1 Revision Cards- Cooking and Communicating using waves

P1 revision cards for cooking and communicating using waves

  • Created by: Eleanor.1
  • Created on: 21-04-14 14:49

Cooking with Waves

  • Infrared (non-ionising waves that produce heat) radiation does not penetrate food easily.
  • Microwaves (non-ionising waves used in satellite and mobile phone networks- also in microwave ovens) penetrate up to 1cm of food.
  • Microwaves can penetrate glass or plastic. They are reflected by shiney metal surfaces.
    • Special glass in a microwave oven door reflects microwaves.
    • They can cause body tiddue to burn.
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Electromagnetic Spectrum

  • Energy is transferred by waves:
    • The amount of energy depends on the frequency or wavelength of the wave.
    • High frequency waves transfer more energy.
  • Normal ovens cook by infrared radiation:
    • Energy is absorbed by the surface of the food.
    • The kinetic energy of the  surface food particals increases.
    • The rest of the food is heated by conduction.
  • Microwave ovens cook food by microwave radiation:
    • The water or fat molecules in the outer layers of the food vibrate more.
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Microwave Properties

  • Microwaves have wavelengths between 1mm and 30 cm.
  • Mobiles use longer wavelengths than microwave ovens.
    • Less energy is tranferred by mobile phones.
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Microwave Communication

  • Microwave radiation is used to communicate over longer distances.
  • The transmitter and reciever must be in line of site.
    • Aerials are usually on top of high buildings.
  • Satellites are used for microwave communication.
    • The signal from the Earth is recieved, amplified, and re-transmitted back to Earth.
    • Satellites are in line of sight becuse there are no obstructions in space.
    • Large aerials can handle thousands of phone calls and television channels at once.
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Microwave Communication 2

  • There are concerns about the use of mobile phones and where phone masts are situated.
  • Scientists publish studies of their findings so others can check their findings.
  • Signal strength of mobile phones can change over longer distances.
    • Microwaves do not show much diffraction (the spreading out of a wave when it passes through a gap or around an edge.)
    • Bad weather conditions and large areas of water can scatter the signals.
    • The shape of the Earth limits the line of site so transmitters have to be on tall buildings or close together.
  • Mobile phones can interfere with sensitive equiptment:
    • They are banned on planes and in many hospitals.
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