Electric current with respect to ground. Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference across the two points. Introducing the constant of proportionality, the resistance, one arrives at the usual mathematical equation that describes this relationship: where "I" is the current through the conductor in units of amperes, "V" is the potential difference measured "across" the conductor in units of volts, and "R" is the resistance of the conductor in units of ohms. More specifically, Ohm's law states that the "R" in this relation is constant, independent of the current. In
Current source the load resistance approaches zero (a short circuit). Such a theoretical device would have a zero ohm output impedance in series with the source. A real-world voltage source has a very low, but non-zero output impedance: often much less than 1 ohm. Conversely, a current source provides a constant current, as long as the load connected to the source terminals has sufficiently low impedance. An ideal current source would provide no energy to a short circuit and approach infinite energy and voltage as the load resistance approaches infinity (an open circuit). An "ideal" current source has an infinite output impedance