On this picture of Flodigarry Island off the coast of Skye, I have shown WAVEFRONTS in dotted yellow lines and RAYS as red arrows. They are PROGRESSIVE WAVES, moving from A down the picture. At first, the wavefronts are straight. These are called PLANE WAVES. The waves experience DIFFRACTION at the ends of the island and are transformed into semi-circular wavefronts. You now end up with two sets of wavefronts heading towards each other from opposite directions. They will overlap at B. This is called SUPERPOSITION. When this happens, you get INTERFERENCE between waves. If a peak of one wave meets the peak of the other wave, you get a single peak twice as high. This is called CONSTRUCTIVE INTERFERENCE. If the peak
of one wave meets the trough of the other wave, the waves totally cancel each other out. We call this DESTRUCTIVE INTERFERENCE.
