Unit 1.6

• 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.
• Conditions for total internal reflection

  • 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. Signal travels to the satellite

  2. Signal travels back to Earth

  3. Signal travels to the next satellite
• The total distance the signal travels is 4 times the distance from the base station to the satellite
• 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.
• Endoscopes vs CT scans

  • Endoscopes 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, but pose a higher risk due to the X rays
• Optical fibres

  Use total internal reflection 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.