Double Slit Experiment
Take a hair and try to measure the width with a ruler? Does this work … no! The hair is very thin … less then one millimeter or 1/32″ and much too thin to use a ruler.
One method that scientist use to measure very small objects is diffraction and interference. This method uses what scientists have learned from the “Young’s Double Slit Experiment”. The laser diffracts around the hair and creates an interference pattern on the wall. We can then measure the peaks in the interference pattern and calculate the width of the hair.