The Kibble balance: A low-cost implementation as an undergraduate laboratory experiment or demonstration

We describe the fabrication and implementation of a dynamic Kibble balance experiment to enable the measurement of mass without the use of a scale, modifying the experimental design of a recently published approach. In this experiment, the voltage induced by a pellet, consisting of two opposed magnets passing through a coil, is used to determine mass via measurements of the induced voltage, pellet velocity, and the current required to levitate the pellet. In particular, we simplified the electronic timing by the use of two coils separated by a known distance to allow the measurement of velocity without the use of photogates. Thus, the total cost for the equipment fabrication is under $25 USD. For data collection, this equipment is then paired with either an oscilloscope, or a smart pulley system, equipment that is available in most first-year physics laboratories. Finally, we use expressions for the induced electromotive force (EMF) of a magnet falling through a coil to fit the distance dependence of the EMF generated during the velocity mode part of the experiment.