The quantity, rate of flow, and driving force for electrons are described by the following basic quantities. Charge is an amount of electrons. One amp is equal to one coulomb per second. One volt is defined as the potential difference that requires one joule of energy to move one coulomb of charge. Voltage is always measured relative to some other point in a circuit, e.g., the potential across a resistor.
Impedance is the degree to which an electronic component impedes the flow of current.
In general it is a frequency-dependent quantity. The impedance of a resistor is also called its resistance. The impedance of capacitors and inductors is also called their reactance. The definitions of resistance , capacitance , and inductance are included with the discussion of resistors , capacitors , and inductors , respectively.