Electromagnetic waves

Electromagnetic waves

1. The electromagnetic spectrum

   • the electromagnetic spectrum (in order of increasing wavelength: gamma, X-rays, ultraviolet, visible, infrared, microwaves, radio waves.
   • wave speed = frequency X wavelength

2. Light, infrared, microwaves and radio waves

   • white light contains all colours in the spectrum
   • visible light, infrared radiation, microwaves and radio waves are all used for communication

3. Communications

   • radio waves of different frequencies are used for different purposes
   • microwaves are used for satellite TV signals
   • research is needed to evaluate whether or not mobile phones are safe to use
   • optical fibres are thin fibres that are used to transmit signals by light and infrared radiation

4. The expanding universe

   • light from distant galaxies is red-shifted
   • red-shift provides evidence that the universe is expanding

5. The Big Bang

   • the universe started with the Big Bang : a massive explosion from a very small initial point
   • the universe has been expanding ever since the Big Bang
   • Cosmic microwave background radiation (CMBR) is electromagnetic radiation created just after the Big Bang
   • at present CMBR can only be explained by the Big Bang theory