Total Internal Reflection

• Critical angle


  At the critical angle, the light bends along the boundary. If you increase the angle, the light will reflect. This is called total internal reflection.
• Total internal reflection


  • The two conditions required for total internal reflection to occur are:
  • The light must be travelling from a higher optical density towards a lower optical density, for example glass into air.
  • The angle between the normal and the ray of light must be greater than the critical angle.
• Signal travel from A to B via satellite

  1. The signal must travel to the satellite, back to Earth and then to the next satellite as they cannot send signals directly to each other.

  2. The total distance the signal travels is 4 times the distance from the base station to the satellite.
• The total distance the signal travels via satellite is 4 × 36000km = 144000km
• Calculating time for signal to travel from A to B via satellite

  1. time = distance / speed

  2. time = 144 000km / 300 000km/s = 0.48s
• Calculating time for signal to travel from A to B via optical fibre

  1. time = distance / speed

  2. time = 20 000km / 200 000km/s = 0.01s
• Endoscopes


  • Use total internal reflection to investigate specific areas of the body.
  • Light is sent into the body through an optical fibre and reflected back along another optical fibre to a camera located outside the body.
  • They investigate specific areas in detail and are less harmful as no ionising radiation is used.
• CT scans


  • Use X rays to generate more overall images of the body and are in 3D.
  • They give a more overall picture but pose a higher risk due to the X rays.
• Optical fibres


  • Total internal reflection is used to send light along a glass tube reflecting from the side of the tube until it reaches the end.
  • This is very useful to send information quickly over long distances and is used in endoscopes.