English: A general two-compartment model to help illustrate the definition of current sources of sinks. In this two compartment model, the compartments are separated by a semi-conductive barrier (gray). An observer, symbolized by the eye, can "see" only one compartment at a time. Red arrows indicate the direction of flow of positive charges, while black arrows indicate the direction of flow of negative charges. The pink and green backgrounds are meant to symbolize different times, time 1 when currents are flowing in one direction and time 2 when they are flowing in the opposite direction. The difference between the left and right panels is simply the location of the "eye".

A source or a sink is defined by which compartment is viewable by the observer.

• A source is:
  • A flow of positive charges from the "invisible" to the "visible" compartment (i.e. "toward the eye"), or...
  • A flow of negative charges from the visible to the invisible (away from the eye).
• A sink is:
  • A flow of positive charges "away from the eye", or...
  • A flow of negative charges "toward the eye".

Diagram drawn by Synaptidude in CorelDraw!