A simple experimental setup for investigating light diffraction with a thin copper wire and a LED

A simple experimental setup for quantitatively investigating single-slit diffraction is described, which uses only inexpensive materials and can be reproduced at home, making it suitable for distance learning. The theoretical basis exploits Babinet's principle, according to which a thin wire—much easier to obtain than a slit—produces, with a very good approximation, a diffraction pattern which is the same as that produced by the slit. A copper wire is placed directly on the camera of a smartphone, and the resulting photos are quantitatively analyzed with Tracker. As light sources, LEDs of different colors are used.