Activities

1. First, press the Play button to start the simulation running. One thing the simulation can help with is in understanding how this interesting pattern is formed, from two sources that put out identical single-frequency waves. Click-and-drag the yellow dot to change its location on the screen. You should observe that, whenever the yellow point is at a position in which there is a large amplitude displacement, that the path-length difference for that point (shown in yellow at the bottom right) is an integer number of wavelengths (or close to it). In contrast, whenever the yellow point is at a position in which there is generally no displacement (it's always dark there), the path-length difference for that point is an integer number of wavelengths plus half a wavelength (or close to it).
2. Explore different points on the line joining the two sources. In between the sources, along the line joining the sources, you should observe a standing wave, with nodes (zero displacement points) and anti-nodes (maximum displacement points) that are fixed in position. For a node, you should measure a path-length difference that is close to an integer number of wavelengths plus half a wavelength. For the anti-nodes, you should observe a path-length difference that is close to an integer number of wavelengths. Is this what you find? Explain why you will always find an anti-node at the place that is halfway between the two sources.
3. Let's keep exploring what happens along the line joining the two sources, but now place the yellow point on this line, to the right of the source on the right. Adjust the frequency of the waves, or the x-coordinate of one or both of the sources, until the path-length difference is 3 wavelengths. Is constructive interference taking place at the point, or is it destructive interference? What is the distance between the sources (expressed in terms of wavelengths) in this case? Repeat, when the path-length difference is 3.5 wavelengths.
4. The wave speed has a constant value in the simulation. With the wave speed constant, what happens to the wavelength when the frequency is increased? In general, what happens to the pattern when the frequency is increased?
5. In general, what happens to the pattern when the two sources are move closer together?