Topic 11 – Wave Phenomena

1. Topic 11 – Wave Phenomena

2. Standing/stationary waves

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

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

5. 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

6. 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.

7. Boundary conditions

8. 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

9. 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

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

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

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

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