Magnetic Fields, Units, and Perpetual Motion
Did you know that, in 2019, the International System of Units was redefined in terms of seven defining constants of nature? A direct consequence is that the value of the permeability of vacuum is no longer fixed. Did you know that the centimeter-gram-second system (gauss, oersted, emu) is obsolete, no longer supported by any standards organization? Did you ever wonder about the difference between B and H? Do you worry about demagnetizing factors when you make magnetic measurements? Did you know that the sum of three orthogonal demagnetizing factors usually does not equal unity? Do you know how to calibrate magnetometers? Or do you just trust the instrument manufacturer? Did you know that magnetism has been invoked in notions of perpetual motion since the 13th Century and still today? This talk is designed to inform and entertain graduate students, but even senior researchers will be amused.
