Ampere the watt, the ohm and the volt. Rather than a definition in terms of the force between two current-carrying wires, it has been proposed that the ampere should be defined in terms of the rate of flow of elementary charges. Since a coulomb is approximately equal to elementary charges (such as those carried by protons, or the negative of those carried by electrons), one ampere is approximately equivalent to elementary charges moving past a boundary in one second. ( is the reciprocal of the value of the elementary charge in coulombs.) The proposed change would define 1 A as being
Electrical resistance and conductance referred to as a "chordal resistance" or "static resistance", since it corresponds to the inverse slope of a chord between the origin and an "I–V" curve. In other situations, the derivative formula_2 may be most useful; this is called the "differential resistance". In the hydraulic analogy, current flowing through a wire (or resistor) is like water flowing through a pipe, and the voltage drop across the wire is like the pressure drop that pushes water through the pipe. Conductance is proportional to how much flow occurs for a given pressure, and resistance is proportional to how much pressure is required