Electricity and Fluids: An Analogy

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Some folks have a difficult time visualizing and understanding the meaning of important electricity parameters, such as current, voltage, resistance, and capacitance. For these folks, it may be useful to think about the flow of electrons in terms of an analogy. Let’s consider the flow of water.



In this analogy, your battery is a tank of water. The capacity is size of your tank. Now let’s say a tube is connected to a valve at the bottom of the tank. When you open the tank, water rushes through the tube. What is pushing the water through the tube? Pressure. The water flows from high pressure (the bottom of the tank) to low pressure. In this analogy, the pressure is the voltage, and the flow of water is the current. The higher the pressure, the higher the flow of water. Similarly, the higher the voltage, the higher the current.


Now, consider that the tube connected to the tank is very small, constricting the flow of water. In this case, the flow constriction is the electrical resistance. The bigger the tube, the larger the water flow at a given pressure. Similarly, the lower the electrical resistance, R, the higher the current, I, at a given voltage, V. This relationship is expressed mathematically as Ohm’s law:


V = I x R


Finally, let’s consider the amount of power you want to produce from your tank/battery. For a flow of water, the power is a combination of the flow rate and the pressure driving the flow. Similarly, the power, P, produced by an electrical current is the product of the voltage, V, and the current, I:


P = V x I


Since the voltage and current are related through Ohm’s law, it is possible to calculate the power from current and resistance:


P = I^2 x R


Or from the voltage and resistance:


P = V^2 / R