# Topic 11 – Wave Phenomena.

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Topic 11 – Wave Phenomena

Standing/stationary waves

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

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

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

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.

Boundary conditions

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

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

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

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

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

Some standing wave investigations
We are now going to do two investigations involving standing waves