Diffraction
Diffraction is the name given to the interaction between waves and an object. For example in the ripple tank shown opposite an object through whihc the wave cannot travel, causes an obstrcution, past the object the wave spreads in an almost circular pattern. If there is just a slit through which the wave can pass then we see this pattern on either side as the separation distance decreases and approaches the wavelength, the pattern after the slit becomes more and more like a semi-circle. this is observable in light as well as water,