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Reflection

2.7 Non-optical reflection

Describe non-optical reflection that occurs naturally in the environment or that is produced through technological applications. **

1. Non-optical reflection phenomena

The principles of optical reflection examined so far have other applications. We can use this knowledge to understand how other reflecting devices work:

  • other types of electromagnetic emissions:
    gamma rays, x-rays, UV, heat, microwave and radio waves;
  • small, hard objects (non-elastic collisions):
    balls, marbles, discs...

2. Technological applications

A conventional antenna is hardly effective for capturing satellite and television rays because of the huge amount of diffusion these rays undergo during their long journeys. In order to capture these weakly concentrated waves, parabolic antennas are used.

The parabolic dish concentrates the waves by reflecting them towards an antenna. These waves, coming from so far away, are almost parallel on arrival and so are reflected to the focus. By placing the receiving antenna at the focus of the parabolic reflector, the waves are concentrated at the antenna which transforms them into electric impulses.

 

Transmitting antennas on satellites are also placed inside a parabolic dish. The antenna placed at the focus of the curved reflector emits diverging radio waves, but these are reflected parallel to the orientation of the dish. Thus it is possible to direct the emitted waves very precisely.

Racket games, like tennis and badminton, all involve controlling the change in direction of the ball, following the laws of reflection (Careful: when there is a spin on the ball, this effect adds another factor which does not follow the laws of reflection). The accompanying diagram represents the case of a ball thrown, with no spin, at a brick wall.