tag:techtv.mit.edu,:Array/225257720 2009-04-16 11:06:25 -0400 MIT Department of Physics Technical Services Group A laser is directed at an adjustable single slit and then a pinhole and the resulting diffraction patterns can be seen on a screen. <br><br> A laser directed at two slits spaced closely next to each other creates an interference pattern within the diffraction pattern. Shining lasers of different wavelength light shows how the wavelength affects the interference and diffraction patterns. 146 tag:techtv.mit.edu,:Array/225234360 2009-07-21 15:46:49 -0400 MIT Department of Physics Technical Services Group A ripple tank is placed above a mirror and a projection screen. Two synchronous point sources, whose frequency can be varied, tap the surface of the water and produce circular waves. The interference pattern of the waves including the lines of nodes can be observed on the screen. 102 tag:techtv.mit.edu,:Array/225211980 2009-07-22 11:09:55 -0400 MIT Department of Physics Technical Services Group A ripple tank is placed above a mirror and a projection screen. A horizontal bar, whose frequency can be varied, taps the surface of the water and produces plane waves. The waves are incident on a barrier containing an adjustable opening. <br><br> With a narrow single slit opening we see a plane wave emerge as a spherical wave on the other side of the barrier. This can be explained by the <a href="http://en.wikipedia.org/wiki/Huygens_principle">Huygens-Fresnel principle</a> which states that each point in the slit forms its own spherical wavefront source. With a wider slit, more point sources arise, causing interference patterns due to the larger angles involved with a broader spatial distribution of these sources. 186