Pronunciation: [wˈɒt bˈaləns] (IPA) 
Watt balance is a term used in physics to describe a device that measures the Planck constant. It is spelled with a "w" and "t" because it is named after James Watt, the Scottish inventor who developed the steam engine, and balance, which refers to the device's ability to compare the weight of two objects. In IPA phonetic transcription, it would be spelled /wɒt ˈbæləns/, with emphasis on the "w" and "t" sounds.
A watt balance is a precision scientific instrument designed to measure the unit of power known as the watt. It uses the fundamental principles of electromagnetism and mechanics to equate mechanical power with electrical power.
The watt balance operates by comparing the weight of a known mass to the electromagnetic force required to balance it. It consists of a coil of wire placed within a magnetic field and a balance mechanism. The current passing through the coil generates a magnetic field, which interacts with the magnetic field produced by a permanent magnet. As a result, an electrical force is exerted, counteracting the gravitational force acting on the known mass. By manipulating the current, the force can be adjusted until equilibrium is achieved.
The watt balance requires accurate determination of various parameters, including the strength of the magnetic field and the length of the coil. These measurements are crucial for calculating the electrical power corresponding to the mechanical power. By precisely measuring the electrical power, the watt balance enables an accurate determination of the physical constant known as the Planck constant, which plays a fundamental role in quantum mechanics.
The watt balance is employed in metrology laboratories worldwide to redefine the kilogram in terms of fundamental physical quantities. It provides a highly accurate and reproducible method of measuring power, contributing to the advancement of science, industry, and technology.
The word "watt balance" is derived from the name of the unit of power, the watt, and the term "balance". The watt is named after the Scottish engineer James Watt, who made significant contributions to the development of steam engines in the 18th century. A watt balance, also known as a Kibble balance, is a device used to measure the weight of an object by the application of an electromagnetic force. It balances the mechanical weight against the electromagnetic force produced by a current-carrying coil in a magnetic field. The term "balance" refers to the equalization of opposing forces in the instrument. Thus, "watt balance" is named to describe the instrument's function and its connection to power measurement.
