Definition:Ampere

Definition

The ampere is the SI base unit of electric current.

It is defined as being:

The constant current which will produce a force of attraction whose value is $2 \times 10^{–7}$ newtons per metre of length between two straight, parallel conductors of infinite length and of infinitesimal circular cross-section placed one metre apart in a vacuum.

By Force between Infinite Parallel Straight Conductors carrying Steady Current, we have:

$\mathbf F = \dfrac {\mu_0 I_1 I_2} {2 \pi r}$

where:

$I_1$ and $I_2$ denote the current through $s_1$ and $s_2$

$r$ denotes the distance between $s_1$ and $s_2$

$\mu_0$ denotes the vacuum permeability.

Setting $r = 1$ metre, this becomes:

$\mathbf F = \dfrac {\mu_0 I_1 I_2} {2 \pi}$

If $\mathbf F$ is measured in newtons, then $I_1$ and $I_2$ are in amperes.

Symbol

The symbol for the ampere is $\mathrm A$.

Also known as

In the everyday context of electricity as a utility, the word amp is usually used.

Source of Name

This entry was named for André-Marie Ampère.

Sources

• 1964: Milton Abramowitz and Irene A. Stegun: Handbook of Mathematical Functions ... (previous) ... (next): $2$. Physical Constants and Conversion Factors
• 1969: J.C. Anderson, D.M. Hum, B.G. Neal and J.H. Whitelaw: Data and Formulae for Engineering Students (2nd ed.) ... (previous) ... (next): $1.$ Units and Abbreviations: $1.2$ SI units $(1)$ Basic units
• 1976: Ralph J. Smith: Circuits, Devices and Systems (3rd ed.) ... (previous) ... (next): Chapter $1$: Electrical Quantities: Definitions and Laws: The International System of Units
• 1976: Ralph J. Smith: Circuits, Devices and Systems (3rd ed.) ... (previous) ... (next): Chapter $1$: Electrical Quantities: Definitions and Laws: The International System of Units: Table $1$-$1$ Basic Quantities
• 1990: I.S. Grant and W.R. Phillips: Electromagnetism (2nd ed.) ... (previous) ... (next): Appendix $\text A$: Units
• 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): ampere
• 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): ampere