Using Overhead Projector to Simulate X-ray Diffraction Experiments

A demonstration to simulate X-ray diffraction experiments can be performed using an overhead projector. The glass surface of the overhead projector is covered with a piece of cardboard that has an 8-mm circular or square hole in the center. The projector is focused so that a circular, or square, spot is projected onto the screen. In the light-beam path we place a pattern made of a combination of transmission diffraction gratings. The obtained diffraction pattern depends on the combination of diffraction gratings. In a dark room, third-order diffraction spots are visible when relatively good-quality gratings are used. A projection distance of 2.4 m gives an 80-cm diffraction spacing (first order, red band) on the screen. As a classroom activity, the spacing between the lines of a grating or, once the spacing is known, the wavelength of diffracted light can be calculated.