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Topic 11 – Wave Phenomena

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**Standing/stationary waves**

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Interference of waves Remember that when two waves of the same frequency interfere, we can get constructive interference or destructive interference. + = = +

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**Formation of a standing wave**

Standing wave (explanation by superposition with the reflected wave) wave-on-a-string_en

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**Formation of a standing (stationary wave)**

Two waves of same speed and wavelength and equal or almost equal amplitudes travelling in opposite directions superimpose and interfere A standing wave is produced with nodes at points of destructive interference and antinodes at points of constructive interference

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**Travelling waves and standing waves**

Travelling waves transfer energy, standing waves do not. All points on a travelling wave have the same amplitude, in a standing wave they do not. On either side of a node the points on a standing wave are 180° out of phase.

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Boundary conditions

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**Formation of a standing wave by reflection**

A travelling wave is reflected The reflected wave is 180° out of phase with the original wave The two waves travelling in opposite directions superimpose and interfere A standing wave is produced with nodes at points of destructive interference and antinodes at points of constructive interference

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Boundary conditions For a standing wave on a stretched string, there has to be a node at each end 1st harmonic or fundamental 2nd harmonic nodes 3rd harmonic 4th harmonic antinodes

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Boundary conditions For sound waves in a tube it depends on whether the tube is open or closed Standing longitudinal waves

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Boundary conditions For an open tube, there has to be an antinode at each end

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Boundary conditions For a tube closed at one end, there is a node at the closed end and an antinode at the other

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**Some standing wave investigations**

We are now going to do two investigations involving standing waves

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