How do waves change direction?

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How do waves change direction?
« on: 14/12/2010 16:30:03 »
Erick asked the Naked Scientists:
In what ways can waves change direction?

What do you think?
« Last Edit: 14/12/2010 16:30:03 by _system »



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How do waves change direction?
« Reply #1 on: 14/12/2010 18:26:56 »
By reflection, refraction, diffraction, or a willful attitude.


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How do waves change direction?
« Reply #2 on: 14/12/2010 18:47:05 »
The Three main ways that waves change direction (assuming for the sake of simplicity a plane wavefront with waves travelling in a straight line) are reflection, refraction and diffraction.

Reflection is just the result of waves encountering a smooth (compared with the wavelength) surface that does not absorb them and does not allow them to propagate into it (conducting surfaces for electromagnetic radiation rigid surfaces for sound) when the direction of the waves is simply reversed.

Refraction is the result of the plane wavefront passing into a medium with a different propagation velocity at an angle that is not exactly perpendicular to the surface  examples of this are prisms and lenses in optics and water waves turning to come in perpendicular to a slowly shelving beach.  if the velocity is dependant on frequency this can cause waves of different frequency to be deflected differently this is how prisms create a spectrum of white light.  The gravitational bending of light is similar to this.  Another way of looking at this is that waves always follow the easiest route for them to propagate.

Diffraction is a process that happens when waves are partially obstructed by a barrier and some waves go round it.  This causes the waves to in effect bend round the barrier.   A good traditional way of thinking about how waves behave is to think of every point on a wavefront  as being a new source of waves and the waves that reinforce each other dominating.  If the structure is periodic like a set of railings waves of a particular frequency can be deflected in a particular direction.  A diffraction grating can also be used to create a spectrum.

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