NIST researchers have made their most precise measurement yet of Planck’s constant, an important value in science that will help redefine the kilogram. The new NIST measurement of Planck’s constant is 6.626069934 x 10−34 kg·m²/s, with an uncertainty of only 13 parts per billion. The kilogram is currently defined in terms of a physical artifact, but scientists want to replace this with a more reproducible definition based on fundamental constants of nature.
The researchers used a state-of-the-art device called the Kibble balance, which uses electromagnetic forces to balance a kilogram mass. The Kibble balance has two modes of operation: in one mode, an electrical current generates a magnetic field to balance the mass, while in the other mode, the coil is lifted at a constant velocity, inducing a voltage proportional to the magnetic field strength. By measuring the current, voltage, and coil’s velocity, researchers can calculate Planck’s constant.
The new measurement is part of an international effort to redefine the kilogram in terms of fundamental constants of nature. The kilogram is slated for redefinition in November 2018, along with other units in the SI. The new NIST measurement joins a group of other new Planck’s constant measurements from around the world, all of which have such low uncertainty that they exceed the international requirements for redefining the kilogram.
Keywords: Electromagnetic, Constant, Measurement, Kibble, Uncertainty
