This video below nicely demonstrates this using water waves on a pond. You might want to have another look at the pages on interference – all the formulations and concepts are applicable to Young’s double slit experiment. So the patterns you are observing are very similar to those for two sources whose wave radiation interferes together. The sound through each slit diffracts and radiates rather like two point sources. In fact, you can generate the same patterns by placing two sources where the slits are. To the right of the slits, the waves interfere with each other. Is there a pattern? What creates this? Is the amplitude larger at some places than others? Have a look at what is happening to the right of the slits. The experiment is named after the guy who first carried it out – Young’s double slit experiment. What happens if there are two or more slits? We’ll end up with two or more diffracting waves, which we might expect to interfere with one another.īelow is a simulation of diffraction through two slits. So far we’ve only considered the case of a single slit or gap for the wave to pass through. The video below shows how you can use this method to work out how wavefronts are altered by a slit.ĭiffraction Through Two Slits Young’s Experiment For example – if you dropped a number of pebbles in a straight line, all in one go at exactly the same time, a straight (in science-speak plane) wavefront would be created. These wavelets superimpose and interfere to form more complicated wavefronts.

A wavelet can be described as a circular wave much like the ripple you would get from dropping a small pebble into a pond. Huygens argued that a wavefront could be modelled as a series of wavelets. One way to explain diffraction is to use a mathematical method invented by 17th century physicist Christiaan Huygens. When the gap size is smaller than the wavelength (top movie), more diffraction occurs and the waves spread out greatly – the wavefronts are almost semicircular. When the gap width is larger than the wavelength (bottom movie), the wave passes through the gap and does not spread out much on the other side. slit is narrower than the wavelength Gap width = two wavelengths i.e. When the size of the gap changes, how does this change the diffraction of the wave? When does maximum diffraction occur? (Think about your previous findings on the diffraction of sound around an obstacle).

The difference between the movies is the size of the gap.

This is shown in the two animations below. Diffraction also occurs when a wave passes through a gap (or slit) in a barrier.

Andaaz movie youtube