The simulation above is intended to show how the process of sound wave resonance in air columns works. When a sound wave travels down an air column and reaches the other end, some of the wave reflects back. This occurs whether the other end of the tube is closed or open. If the end is closed, the wave inverts (because it has hit a more rigid medium). If the end is open (less rigid medium), the wave reflects back upright. The reflected wave reflects again when it reaches the other end of the tube, and the process repeats itself again and again. In the simulation, the original wave and its first five reflections are shown. The thickest blue wave is the original wave. The thickest orange wave is the first reflection. The thinner blue and orange waves are all subsequent reflections. The blue waves are all the waves moving to the right, the orange waves are those moving to the left. Resonance occurs when all of the (right moving) blue waves overlap and all of the (left moving) orange waves overlap. When this happens all of the waves moving to the right constructively interfere and all those moving to the left also constructively interfere. The overall interference causes a strong standing wave to develop in the tube and the sound gets louder. As you will be able to see by experimenting, this happens when the length of the tube matches up with the wavelength in just the right proportions. Adjust the length of the tube and the wavelength to verify that resonances occur as shown on the last two pages. |