Waves

Waves

1. EM Waves

   • Gamma radiation
     • Wavelength = < 1nm
     • Source = Radioactive decay of a nucleus
       • Detected using Geiger counter, film or ionisation chamber
     • Used in medical imaging, therapy, sterilisation of medical instruments
   • X-Rays
     • Wavelength = < 1nm
     • Source = Inner shell atomic electron transitions
       • Detected using Geiger counter, film or ionisation chamber
     • Used in X-ray imaging in medicine and dentistry
   • Ultraviolet
     • Wavelength = 1 - 400nm
     • Source = Atomic electron transitions
       • Detected using photocell or film
     • Used in sun beds, security markers (counterfeit bank notes)
   • Visible
     • Wavelength = 400 - 700nm
     • Source = Outer-shell atomic electron transitions
       • Detected using eye, film, CCD or photocell
     • Used in cameras and eyes (to see)
   • Infra-red
     • Wavelength = 700nm - 1mm
     • Source = Vibrations of atoms and molecules
       • Detected using a thermopile or solid state detectors
     • Used in fibre optic communications and thermography in mediciene
   • Microwave
     • Wavelength = 1mm - 0.1m
     • Source = Electrons in resonant cavities, e.g. magnetron valve
       • Detected using a microwave diode
     • Used in cooking, satellite communications
   • Radio and TV
     • > 0.1 m
     • Source = Electrons accelerated and decelerated in an aerial
       • Detected using an aerial
     • Used in communications

2. Definitions

   • Wavelength
     • The distance between 2 equal points on a wave e.g. trough + trough or crest + crest
     • Symbol = λ
     • Unit = m
   • Amplitude
     • The distance between the centre and either the crest or trough of a wave (the maximum disturbance cause by a wave
     • Symbol = a
     • Unit = m
   • Frequency
     • The number of waves occurring over a time period
     • Symbol = f
     • Unit = Hz
   • Period
     • The amount of time taken for one wave to pass a point
     • Symbol = T
     • Unit = s

3. Transverse

   • A wave that is perpendicular to the energy flow

4. Longitudinal

   • A wave that is parallel to the energy flow