(Image: Water Flow- DC Flow Analogy)
Each quantity and each operational relationship in a battery-operated DC circuit has a direct analog in the water circuit. The nature of the analogies can help develop an understanding of the quantities in basic electric ciruits. In the water circuit, the pressure P drives the water around the closed loop of pipe at a certain volume flowrate F. If the resistance to flow R is increased, then the volume flowrate decreases proportionately.
(Image: Water Pump-Battery Analogy)
A battery is analogous to a pump in a water circuit. A pump takes in water at low pressure and does work on it, ejecting it at high pressure. A battery takes in charge at low voltage, does work on it and ejects it at high voltage.
(Image: Constriction in Water Pipe- Resistor in Circuit Analogy)
The resistance to flow represented by a severe constriction in a water pipe is analogous to the resistance to electric current represented by a common electric "resistor".
(Image: Reservoir- Ground Analogy)
The function of a ground wire in an electric circuit is in many ways analogous to the reservoir attached to the water circuit. Once the pipe is filled with water, the pump can circulate the water without further use of the reservoir, and if it were removed it would have no apparent effect on the water flow in the circuit.