Determining the value of the fine-structure constant from a current balance: getting acquainted with some upcoming changes to the SI

TL;DR

This paper discusses the upcoming changes to the SI units, especially the definitions of the ampere and kilogram, and explores their implications for electrical metrology using a current balance as an example.

Contribution

It provides an analysis of how the revised SI definitions impact electrical measurements and clarifies the interpretation of current balance results under new standards.

Findings

Revised SI will fix the elementary charge and Planck constant values.

The changes will cause negligible but necessary adjustments in SI electrical unit conversions.

Implications for electrical metrology are illustrated through current balance analysis.

Abstract

The revised International System of Units (SI), expected to be approved late in 2018, has implications for physics pedagogy; the ampere definition which dates from 1948 will be replaced by a definition that fixes the numerical value of the elementary charge, e, in coulombs. The kilogram definition which dates from 1889 will be replaced by a definition that fixes the numerical value of the Planck constant, h, in joule seconds. Existing SI equations are completely unaffected. However, there will be a largely-negligible, but nevertheless necessary, change to published numerical factors relating SI electrical units to their corresponding units in the Gaussian and other CGS systems of units. The implications of the revised SI for electrical metrology are neatly illustrated by considering the interpretation of results obtained from a current balance in the present SI and in the revised SI.