Equation 1 · From Origins to Frontier: A History of Scientific Instruments and Metrology
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Symbol g
g is part of the quantity the equation computes from the expression on the right.
Symbol U
U is an input to the expression that computes the quantity on the left.
=
The expressions on both sides represent the same quantity under the stated assumptions.
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Because voltage and resistance can themselves be measured to extraordinary precision using quantum electrical effects (the Josephson effect and the quantum Hall effect), a Kibble balance effectively measures mass in terms of the Planck constant, h. The relationship, in its simplified form, is: . where m is the test mass, g the local gravitational acceleration (independently and precisely measured at the balance’s location), v the coil’s velocity in the moving phase, and U and I the voltage and current measured electrically. Combined with the quantum electrical measurements of U and I in terms of h , this equation is what let NIST’s NIST-4 Kibble balance measure the Planck…
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Because voltage and resistance can themselves be measured to extraordinary precision using quantum electrical effects (the Josephson effect and the quantum Hall effect), a Kibble balance effectively measures mass in terms of the Planck constant, h. The relationship, in its simplified form, is: . where m is the test mass, g the local gravitational acceleration (independently and precisely measured at the balance’s location), v the coil’s velocity in the moving phase, and U and I the voltage and current measured electrically. Combined with the quantum electrical measurements of U and I in terms of h , this equation is what let NIST’s NIST-4 Kibble balance measure the Planck constant to within about 13 parts per billion in 2017 — precise enough to underwrite the redefinition that followed [ 5 ] . The BIPM operated its own Kibble balance program in parallel, one of several national and international efforts converging on compatible values of h ahead of the vote [ 5 ] .
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