ABSTRACT
It is extraordinary how few people have seen diffraction phenomena, except perhaps the haloes produced by a steamedup window when a distant street light is viewed through it, or the two-slit pattern ( Young's fringes). (I should perhaps point out here that, in my terminology, diffraction occurs when a wave interacts with an object, e.g. at the double slit, and the resulting scattered waves interfere to produce a pattern on the screen.) But it is very easy to demonstrate a whole range of diffraction phenomena if a simple closed-circuit television is available. Because a great many of my lectures are away from my base I have devised the lightweight, portable substitute for an optical bench that was described in Demonstration 2.3, p. 65, and is illustrated again in figures 2.10 and 2.11. The objects, as before, are photographic reductions on to glass slides
with an overall diameter of about 3 mm. A glass screen with a finely ground surface is placed about 1-1.5 m on the far side of the object and, without any further lensesy a diffraction pattern of sorts can be seen on it.
