Demonstration model of a moving iron ammeter. As the current through the coil increases, the plunger is drawn further into the coil and the pointer deflects to the right.
The ampere (
SI defines ampere as follows:
The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed one meter apart in vacuum, would produce between these conductors a force equal to ×10−7 newton per metre of length. 2
The old definition (valid until 1948) is:
The ampere is equivalent to one
The ampere should not be confused with the
The SI unit of charge, the
In general, charge Q is determined by steady current I flowing for a time t as Q = It.