Electromagnetic waves

13.1 The electromagnetic spectrum 

• Electromagnetic waves are electric and magnetic disturbances that can be used to transfer energy from a source to an absorber. They don't transfer matter, the energy they transfer depends on the wavelength of the wave
  • Radio Waves      Real             Wavelengths as long as 10km
  • Microwaves        Monkeys
  • Infrared               Insist
  • Visible light         Very             Can be seen my humans
  • Ultraviolet           Useful
  • X-rays                 X-mas          Wavelengths as short as a millionth/millionth of a mm
  • Gamma rays       Gifts
• Travel at a speed of 3.0 x 10^8 m/s through a vacuum or space
• wave speed (m/s)  = frequency (Hz)  x  wavelength (m)
• The shorter the wavelength, the higher the frequency. As frequency increases, so does energy

13.2 Light, infrared, microwaves, radio waves

Light

• Light from lamps and sun = white light -- because it has all the colours of the visible spectrum in it. Wavelength increases from violet to red 
• ROYGBIV

Infrared radiation - all objects emit infrared radiation

• The hotter an object, the more infrared radiation it emits
• Infrared radiation is absorbed by skin. It can damage, burn or kill cells as it heats them
• Optical fibres in communication systems tend to use IR, not visible light because IR is absorbed less than visible light in glass fibres
• Remote control handsets for TV transmit signals carried by IR. Pressing the buttons sends a sequence of IR pulses. IR is used because suitable IR pulses can be easily made/detected
• IR can be used to see people and animals in the dark
• IR easily heats things 
  • electric heaters emit IR
  • electric cookers that have halogen hobs heat food faster as they're designed to emit more IR than ordinary hobs
• To compare emission of 2 surfaces, measure how fast it takes for 2 cans of hot water to cool. Use 1 shiny and light can and 1 dark and matt. To compare absorption measure how fast 2 cans of cold water heat up when put in sunlight

Microwaves

• Used for communications, e.g. satellite or phone signals, because they can pass through the atmosphere and reach satellites above the earth
• Heat food faster than normal ovens because they can penetrate food and are absorbed by the water molecules in food. Oven doesn't absorb microwaves as it doesn't contain water molecules

Radio waves

• Frequency ranges from 300,000 Hz to 3000 million Hz 
• Used to carry radio, TV and phone signals
• Microwaves and radio waves can be…