Standing waves

Standing waves, also called stationary waves are the result of wave interference and reflection.

A very common way to create standing waves is to use a rope.

You can have someone hold one end of the rope at a fixed position or you can tie the rope to the wall. The point is to make sure that one end of the rope is fixed in place or cannot move.

What will happen when you shake the free end up and down and creating a wave as a result?

Because the wall is too rigid to shake, the wave will be reflected back to you. 

The wave that goes toward the fixed position is called incident wave and the wave that comes back to you is called reflected wave. Below, we show the incident wave in blue and the reflected wave in green.

Standing waves

A naturally occuring phenomena in standing waves is that certain parts of the rope will look like dots. We call these nodes and show them with black dots. 

Something important to keep in mind is that at these nodes, the string never moves.

The red line is the resultant wave. Since the incident wave and the reflected wave are out of phase with each other, the resulting wave is a straight line or a wave with zezo amplitude.  

The incident wave and the reflected wave can also be in phase with each other as well as you can see in the next graph.

Standing waves

Halfway between adjacent nodes are antinodes. These are just positions with the maximum amplitudes.


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