P3- medical physics

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  • part of electromagnetic spectrum
  • high frequency and short wave length (about same diameter as an atom)
  • they effect photographic film in the same way as light
  • they are absorbed by metal and bone
  • they are transmitted by healthy tissue
  • they are ionising and can damage living tissue
  • used to check for fractures or dental problems
  • charged coupled devices make electronic images of x ray
  • Ct scanner are xrays that produce a cross section of the body (3d) 
  • soft tissue and organs do not show up so to make it show up you must drink a contrast medium that can be aborbed by the xray
  • workers must wear film badges or stand behind a screen to protect themselves
  • xrays can be used to treat cancerous tumours


  • human ear can detect sound waves with frequencies between 20Hz and 20000Hz
  • sound waves higher than 20000Hz are ultrasound waves
  • when the wave meets a boundary between two different materials e.g. tissue and bone part of the wave is reflected and travels back to a detector, it can calculate how far away it is
  • distance= speed x time
  • it is non ionising
  • used for scanning
  • used to shatter kidney stones
  • can detect soft tissue

refractive index

  • refraction is the change of direction of light as passes from one substance into another
  • it happens because waves change speed as they cross a boundary
  • no change if light is travelling along the normal
  • refractive index of a substance is the measure of how much of the substance  can refract a light ray
  • refractive index= sin i / sin r

the endoscope

  • critical angle is the angle of insidence of a light ray in a transparent substance which produces refraction along the boundary
  • refractive index= 1/sin c
  • an endoscope is a device used to look inside a patients body without cutting it open
  • endoscope contains bundles of optical fibres
  • optical fibres are very thin, flexible glass fibres- visible light can be sent…


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