William Thomson, Lord Kelvin
electromagnetism
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Ampere balance
- To measure the ampere,
- slide a weight on a scale
- to balance the current to be measured
- coiled against the weight.
Ampere calculation
- The strength of the current
- when the weight is balanced
- is proportional to the product
- of the square root of the weight
- and its displacement
- from its zero position.
Balance
- Nothing is that delicately balanced
- that the result comes from a simple equation.
- The scale must be level; we must know precisely
- the dimension and winding of the coil;
- and how do we measure the mechanical rigidity
- of linkages and pivots?
- In balancing a current against a weight,
- either current or weight might be off.
- We should apply Bayes’ theorem
- and balance the significance of what we know
- against the weight of what we don’t know.
The Kibble balance is seen as a more accurate version of the Ampere balance even though Kibble’s purpose was to measure a weight and Kelvin’s purpose was to measure a current.
See also in The book of science:
Readings on wikipedia:
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