Recent news items about the oil slick on the River Torrens reminded me of my Bairnsdale High School physics prac to measure the dimensions of a molecule.
Count the number of oil drops needed to measure 1 cc of a low viscosity oil; divide the 1 cc (or 1000 cubic millimetres) by the number of oil drops to calculate the average volume of one oil drop; sprinkle talcum powder over the surface of a shallow ripple tank full of water; place one drop of the oil in the center of the powdered surface. The oil spreads in a roughly circular manner pushing the talc out to surround its perimeter. Several estimates of the dispersed oil drop’s diameter are used to calculate its area. Assuming the oil slick has spread until it is one molecule thick, (and keeping units the same) divide the volume of one oil drop by the oil slick’s area to calculate the thickness of the oil slick and thus the dimension/s of an oil molecule. A most memorable experiment.
aussiemathstutor 