P1 Chapter 6

P1 Chapter 6

1. The Electromagentic Spectrum

   • The electromagnetic spectrum (in order of decreasing wavelength, increasing frequency and energy) is...
     • - Radio Waves
       • - Microwaves
         • - Infrared Radiation
           • - Light
             • - Ultraviolet
               • Gamma rays and radiation X-rays
   • The wave speed equation is used to calculate the frequency or wavelength of electromagnetic waves.
     • Speed = Frequency x Wavelength

2. Light, Infrared, Microwaves and Radio Waves

   • White light contains all the colours of the visible spectrum
   • Infrared radiation is used for carrying signals from remote handsets and inside optical fibres.
   • We use microwaves to carry satellite TV programmes and mobile phone calls.
   • Radio waves are used for radio and TV broadcasting, radio communicating and mobil phone calls.
   • Different types of electromagnetic radiation are hazardous in different ways.
     • Microwaves and radio waves can cause internal heating.
     • Infrared radiation can cause skin burns.

3. Communications

   • Radio waves of different frequencies are used for different purposes because the wavelength (and therefore frequency) of waves affects...
     • - How far they go
     • - How much they spread
     • - How much information they carry
   • Microwaves are used for satellite TV signals
   • Further research is needed to evaluate whether or not mobile phones are safe to use
   • Optical fibres are very thin transparent fibres that transmit signals by light and infrared radiation

4. The Expanding Universe

   • The red-shift of a distant galaxy is the shift to longer wavelengths of the light from it because the galaxy is moving away from us.
     • The light waves are stretched out if the star or galaxy is moving away from us. The wavelength of the waves is increased.
   • The faster a distant galaxy is moving away from us, the greater the red-shift is.
     • All distant galaxies show a red-shift. The further away a distant galaxy is from us, the greater the red-shift is.
   • The distant galaxies are all moving away from us because the universe is expanding.

5. The Big Bang

   • The universe started with the Big Bang, a massive explosion from a ver small 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.
   • CMBR can only be explained by the Big Bang theory.