June 15, 2006
The "e over m" experiment
Two nights ago, in physics lab, we replicated a version of the famous "e over m" experiment of J.J. Thompson, to experimentally determine the ratio of the charge of an electron to its mass, using a Helmholtz coil apparatus:
I took this grainy shot in relative dark with my Treo 650 cellphone, since the flash on my Sony would have been disruptive. This is a transfixing sight: a beam of electrons fluorescing in a rarified Helium tube, produced by a thermionic emission apparatus, made circular by a nearly uniform B-field.
I am fortunate to have a lab partner - an earnest young Japanese guy - who doesn't mind that we deliberately stick around to the bitter end doing these experiments, while many of our classmates try to finish early and leave. These experiments are things of grace and beauty, and should be savored and appreciated. Oh, and it helps that we generally get very good agreement with theory in our experiments by doing so: we were within 3.12% of the theoretical electron charge to mass ratio. On nights like this, I walk home from lab feeling more content than I can describe.
Posted by Russell Whitaker at June 15, 2006 12:55 AM | TrackBack