INTERFERENCE.

Film Loop: Single Slit Diffraction

Length: 3:30 Min., Black and White, No Sound

With the slit width held constant, the wavelength is first decreased from about the size of the slit width to 1/4 that length, and is then increased again to the original wavelength. Next, holding the wavelength constant, the slit width is increased from slightly greater than the wavelength to about 5 times that width. In the last sequence the slit width is about 15 times the wavelength.

APPARATUS. A long vibrating bar was used to generate the periodic straight waves. An abnormally large wave amplitude was generated so that the diffracted wave on the far side of the slit was easily visible. The water depth was about 0.8 inch. The metal barrier protruded above the water surface.

NOTES. In the diffraction pattern, as in interference phenomena (see Film-Loop 80-240), the positions of nodes and maxima depend on both the slit width and the wavelength. In the last sequence one sees strong straight wave fronts beyond the slit, and the diffraction effects are relatively less significant. Even if the slit were very much wider than shown, there would still be diffraction effects at the edge of the slit; see Film-Loop 80-244. Multiple slit diffraction is shown in Film-Loop 80-243.

In order to prevent stroboscopic effects in the projected picture the sequences were photographed with a high speed camera; the projected phenomena are slowed down by about a factor of 3.