Everything about The Ampere totally explained
The
ampere, in practice often shortened to
amp, (symbol: A) is a unit of
electric current, or amount of
electric charge per second. The ampere is an
SI base unit, and is named after
André-Marie Ampère, one of the main discoverers of
electromagnetism.
Definition
The ampere is a constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular
cross section, and placed 1
metre apart in a vacuum, would produce between these conductors a force equal to 2×10
–7 newton per metre of length. For a description of this force law, see Serway. See also
Ampère's force law.
The ampere is a
base unit, along with the
metre,
kelvin,
second,
mole,
candela and the
kilogram: it's defined without reference to the quantity of
electric charge.
The unit of charge, the
coulomb, is defined to be the amount of charge displaced by a one ampere current per unit time of one
second. That is, in general, charge
Q is determined by steady current
I flowing per unit time
t as:
»
Realization
The ampere is most accurately realized using a
watt balance, but is in practice maintained via
Ohm's Law from the units of
EMF and
resistance, the
volt and the
ohm, since the latter two can be tied to physical phenomena that are relatively easy to reproduce, the
Josephson junction and the
quantum Hall effect, respectively. The official realization of a standard ampere is discussed in
NIST Special publication 330 Barry N Taylor (editor) Appendix 2, p. 56
.
Proposed future definition
Since a coulomb is approximately equal to 6.24150948×10
18 elementary charges, one ampere is approximately equivalent to 6.24150948×10
18 elementary charges, such as
electrons, moving past a boundary in one second.
As with other
SI base units, there have been proposals to redefine the
kilogram in such a way as to define some presently measured
physical constants to fixed values. One proposed definition of the kilogram is:
This redefinition of the kilogram has the effect of fixing the
elementary charge to be
e = 1.60217653
C and would result in a functionally equivalent definition for the
coulomb as being the sum of exactly 6 241 509 479 607 717 888 elementary charges and the ampere as being the electrical current of exactly 6 241 509 479 607 717 888 elementary charges per second. This is consistent with the current 2002 CODATA value for the elementary charge which is 1.60217653×10
-19 ± 0.00000014×10
-19 C.
CIPM recommendation
International Committee for Weights and Measures (CIPM) Recommendation 1 (CI-2005):
Preparative steps towards new definitions of the
kilogram, the ampere, the
kelvin and the
mole in terms of fundamental constants
The International Committee for Weights and Measures (CIPM),
- approve in principle the preparation of new definitions and mises en pratique of the kilogram, the ampere and the kelvin so that if the results of experimental measurements over the next few years are indeed acceptable, all having been agreed with the various Consultative Committees and other relevant bodies, the CIPM can prepare proposals to be put to Member States of the Metre Convention in time for possible adoption by the 24th CGPM in 2011;
- give consideration to the possibility of redefining, at the same time, the mole in terms of a fixed value of the Avogadro constant;
- prepare a Draft Resolution that may be put to the 23rd CGPM in 2007 to alert Member States to these activities;
Further Information
Get more info on 'Ampere'.
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