I’ve been studying electricity lately and it has been quite hard to understand the terminology, and picturing it in my mind. After struggling to understand what each property of electric currents meant, I found an analogy that related electric current to water flow. I am not sure if this analogy is 100% accurate, but it sure has helped me understand the complex (at least for young, starter scientist like me) topic of electricity. This far I have managed to relate in the analogy that:


Current (Amps)(A)-------Flow rate (Volume/Time)

Resistance (Ohms)(Ω)----pipe size (Inches)

Voltage (Volts)(V)------Water pressure (psi)

But I am still missing properties like charge. What properties am I missing? How could it be related to water flow? If it can’t be related, can you please give me a short definition and explanation to better grasp the concept? Please include units in both sides of the analogy. Also, please keep the answer short and simple for us, the inexpert scientist (including me) that struggle to grasp the concept.

Thanks a bunch for your expert help

It is kind of discussed in these articles:

Flow of water and flow of electrons, how this analogy works?

Power in hydraulic analogy

But I couldn’t find (or understand) the answer provided in them.


1 Answer 1


Your analogy is legitimate for understanding the basics of circuits. You might find picturing a compressible fluid like air slightly more helpful than a fluid like water. In such an analogy, above average air density is like excess positive charge and below average air density is like excess negative charge. The charge is the fluid.

Coulombs = gallons

Battery = pump. But it is a pump that uses a constant amount of "effort", producing more or less flow depending on the resistance it encounters.

Diode = valve, only allows flow in one direction.

Capacitor = A rubber barrier inside a pipe. It stretches some as it stops the flow. The greater the pressure difference the more it stretches. Capacitance is like the inverse of the spring constant of this membrane.

I don't think there are good analogies with fluids for phenomena based on the magnetic fields of circuits - induction, transformers, motors, etc. Inductance is a bit like the inertia of the fluid, but I'm not sure it is helpful to push on that analogy.

  • $\begingroup$ Thanks a bunch! It was very clear but I was left with a couple of questions. What is the difference between coulombs (Gallons) and current (Flow)? Are coulombs the actual “volume” (amount) of electrons and current the flow of those electrons? What is the point of stretching the “rubber barrier” in a capacitor? Also, can you please make a small list of the terms that don’t apply to the analogy so I can further investigate them? $\endgroup$ Apr 23, 2014 at 2:18
  • $\begingroup$ Also, when you say under capacitor “the greater the pressure difference the more it stretches” do you mean the more voltage flow, the more it “stretches?" $\endgroup$ Apr 23, 2014 at 2:35
  • $\begingroup$ @JPhysicsFM Coulombs (C) is the unit of charge. The analogy is: Charge (Coulombs) to Volume (gallons or cubic inches). Current is rate at which charge moves. Units of current are coulombs/second which by definition is an Ampere (Amp, A). Volumetric flow rate is the rate at which volume moves, in units of gallons per second or cubic inches per second. $\endgroup$
    – DavePhD
    Apr 23, 2014 at 17:37

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