Kibble balance

Kibble balance is a highly precise measuring instrument used to determine the mass of an object through the electrical force needed to counteract its weight. It is named after Bryan Kibble, a British physicist who invented the balance in 1975. The Kibble balance is a cornerstone in metrology, providing a way to link mass to fundamental constants of nature, specifically the Planck constant, following the redefinition of the International System of Units (SI) in 2019.

Principle of Operation

The Kibble balance operates on the principle of electromagnetic force restoration. It measures the weight of an object by opposing it with an electromagnetic force produced by an electric current running through a coil in a magnetic field. The balance has two operational modes: weighing and moving. In the weighing mode, the force needed to balance the mass of the object is determined. In the moving mode, the velocity of the coil moving through the magnetic field is measured. These two measurements allow for the calculation of the Planck constant and, consequently, the precise measurement of mass based on fundamental physical constants.

Historical Background

The development of the Kibble balance marked a significant advancement in the field of metrology. Before its invention, the kilogram was defined by a physical object, the International Prototype Kilogram (IPK), a cylinder made of a platinum-iridium alloy. However, the mass of the IPK was found to vary over time, leading to the search for a more stable definition of the kilogram. The Kibble balance provided a solution by enabling the kilogram to be defined in terms of the Planck constant, a fundamental constant of nature that does not change.

Impact on the Redefinition of the Kilogram

In 2019, the definition of the kilogram was officially changed from being based on the IPK to being defined in terms of the Planck constant. This redefinition was made possible by the Kibble balance, which allows for the precise measurement of the Planck constant. The new definition provides a more stable and accurate standard for measuring mass, with far-reaching implications for science and technology.

Applications

The Kibble balance is used in national metrology institutes around the world to calibrate secondary standards of mass. Its precision and stability also make it an essential tool in scientific research, where accurate measurements of mass are crucial.

Future Developments

Research and development efforts continue to focus on improving the precision and accuracy of the Kibble balance. Advances in materials science, electronics, and quantum mechanics may lead to further enhancements in its performance. The ongoing evolution of the Kibble balance will contribute to the progress of precision measurements and standards in metrology.

See Also

• Metrology
• International System of Units
• Planck constant
• International Prototype Kilogram

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  NIST-4 Kibble balance

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  Ampere balance 1927

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  Kibble balance in weighing mode

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  The Kibble balance in moving mode

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  Michelson Interferometer Laser Interference Fringes