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Ampere

lastmod 2025-11-05created 2020-09-229 edits

The ampere is the SI base unit used to measure electric current. Its symbol is A, and its abbreviation is amp. The current definition was adopted at the 9th General Conference on Weights and Measures in 1948. It is named after André-Marie Ampère.

The so-called "international" electrical units for current and resistance were introduced at the International Electrical Congress held in Chicago in 1893, and the definitions of the "international ampere" and "international ohm" were ratified at the International Conference in London in 1908. Although there was already a unanimous desire at the 8th CGPM (1933) to replace the "international units" with so-called "absolute units," the decision to abolish them was only formally made at the 9th CGPM (1948). At this meeting, the ampere was adopted as the unit of electric current according to the following definition proposed by the CIPM (1946, Resolution 2; PV, 20, 129-137).

Simple brief

The strength of the current flowing per given time is called the ampere (A; current), and its unit is A. A large current can be thought of as 'a large amount of electricity is flowing.' In other words, the container that can hold electricity is that much bigger.

Definition

The ampere is the constant current which, if maintained in two straight parallel conductors of infinite length and negligible circular cross-section placed 1 meter apart in vacuum, would produce between these conductors a force of \(\textstyle 2 \times 10^{-7}\) newtons (N) per meter of length.

Reading the units

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Things to watch out for:

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Volt/Ampere/Watt relationship

Volt

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  • For example, here are 3 waterfalls of different widths and heights.
  • Waterfall 2, whose water is wider, has more force than waterfall 1 of the same height. (Difference in A)
  • Between waterfalls 2 and 3, which have the same width, waterfall 3, which is taller, has more force. (Difference in V)

Ampere

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  • Filling a 100-liter water tank through a 1 cm diameter pipe at a pressure (V) of 10 (①) takes 10 seconds.
  • Increasing the pressure (V) to 20 would take 5 seconds, and widening the diameter to 2 cm also takes 5 seconds (②).
  • When filling the same amount of water in the same time, pressure (V) and diameter (A) are inversely proportional.
  • On the other hand, if the goal is simply to fill it as fast as possible regardless of time, you would raise both pressure and diameter. (③)

Watt

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Categories

Troubleshooting

What if the adapter amplifier is different?

See Adapter#What if the adapter amplifier is different? for details.

See also

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