How Thick is Your Hair? An Interactive Physics Demo for the General Public.

This talk will describe a demo-in-box that can be setup on a standard table and requires a pen laser, a mount, a ruler, and a box (if it's sunny). Participants are invited to pluck a hair, and tape it onto a cardboard mount. The diffraction pattern is observed on a screen and the width of the central bright band is measured. To speed up the process we use a data table to convert the measurement in mm to the hair thickness in micrometers. The participants help update a histogram of all of the hair thickness measurements made during that day. This demo can be used to talk about a variety of different topics depending on the age and sophistication of the audience. We can discuss the meaning of a micrometer, what a histogram shows, the normal distribution, how laser light is different from other light, the shadow of the hair vs the diffraction pattern, Huygens wavelets, and Babinet's principle.