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Encyclopedia > Ampere balance

The ampere balance (also current balance or Kelvin balance) is an electromechanical apparatus used for the precise measurement of the SI unit of electric current, the ampere. It was invented by William Thomson, 1st Baron Kelvin.

The current to be measured is passed in series through two coils, and the force between the two coils is measured. This is used to calculate the magnitude of the current.

The main weakness of the ampere balance method is that the result depends on the accuracy with which the dimensions of the coils are measured. An improved apparatus called the watt balance sidesteps this problem and is now used instead.

Results from FactBites:

 ampere - definition of ampere - Labor Law Talk Dictionary (380 words) In physics, the ampere (symbol: A, often informally abbreviated to amp) is the SI base unit used to measure electrical currents. The ampere is most accurately realised using a ampere balance, but is in practise maintained via Ohm's Law from the units of voltage and resistance, the volt and the ohm. The unit of electric charge, the coulomb, is defined in terms of the ampere: one coulomb is the amount of electric charge (formerly quantity of electricity) carried in a current of one ampere flowing for one second.
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