### Ripple animation

Try dragging the slider to change the size of the gap. How does this affect wave diffraction? This animation ripple animation just a guide – below is a proper mathematical ripple tank simulation of waves passing through a slit. What difference does the length of slit make in terms of diffraction?

When the gap size is larger than the wavelength, the wave passes through the gap and does not spread out much on the other side. When the gap size is equal to the wavelength, maximum diffraction occurs and the waves spread out greatly – the wavefronts are almost semicircular. Huygens argued that a wavefront could be modeled as a series of wavelets. A wavelet can be described as a circular- shaped wave much like the ripple you would get from dropping a small pebble into a pond. These wavelets superimpose and interfere to form more complicated wavefronts.

This slow-motion video shows what happens when a single wavelet is created by a droplet falling into still water. So far we’ve only considered the case of a single slit or gap for the wave to pass through. What happens if there are two or more slits? Below in a simulation of diffraction through two slits.

The experiment is named after the guy who first carried it out – Young’s double slit experiment. Have a look at what is happening to the right of the slits. Is the amplitude larger at some places than others? To the right of the slits, the waves interfere with each other. In fact, you can generate the same patterns by placing two sources where the slits are. The sound through each slit diffracts and radiates rather like two ‘point sources’.