alleryStart learning →Wires of infinite length cannot be built. How is the definition of the ampere realised in a laboratory?
AWith coils of wire a few kilometres apart
BWith a single wire bent into one long loop
CWith two magnets a few centimetres apart
DWith coils of wire a few centimetres apart
Answer & Solution
Correct answer: D. With coils of wire a few centimetres apart
1. The definition of the ampere is stated for parallel conductors of infinite length.
2. Infinite wires are impractical, so a current balance is built instead.
3. That balance uses coils of wire separated by a few centimetres.
4. The force between the coils is measured, and the current is worked out from it.
5. Measuring force between conductors remains the most accurate practical method for the ampere.
_Source: OpenStax College Physics (CC BY 4.0), Ch 22 "Magnetism", section 22.10 Magnetic Force between Two Parallel Conductors_
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