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I'm trying to wrap my head around Voltage and Current. I saw this analogy on a post from another site that seems to make sense:

For circuits I tend to mentally use a "plumbing" analogy. The voltage is like the water pressure, and the current is like the flow.

Reference https://www.physicsforums.com/threads/visual-model-for-voltage.200937/

My struggle is understanding how this analogy would describe something like using a number of lemons in parallel as a battery. I have seen example people provide where a few lemons can be coaxed to produce around 3 volts of energy.

2 AA's can also be coaxed to produce roughly 3 volts of energy. Yet the current from the Lemon batteries is minuscule compared to that of the Alkaline batteries.

So in this analogy applied to those. The Lemon battery has 3v of pressure and low flow (current) and the Alkeline batteries have roughly the same 3v of pressure but considerably faster flow (current).

Is that difference in flow due to resistance in the lemon? I heard if you squish the lemon you get more current out of it. Could just the juice outside of the lemon produce similar Voltage/Current?

How could one using the same analogy above incorporate the cause of the difference in current between the two?

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  • \$\begingroup\$ voltage is like height of water or a featherweight lemon battery and current is the flow due to gravity and pipe size big enough not to restrict flow. the greater the height the faster the flow. but if dealing with feathers or lemons not much is going to flow and is easily stopped. Resistance or its inverse Conductance is like the size of the pipe. so a thin straw has very high resistance. a diode is like a water valve with a spring that only flows in one direction of pressure unless reversed too high and then it breaks down and either fuses open or a short circuit and anything flows \$\endgroup\$
    – Tony Stewart EE75
    Jun 29, 2019 at 1:58
  • \$\begingroup\$ Ohm’s Law is simply with ratio of V/I=R if it is linear. But many things are not. \$\endgroup\$
    – Tony Stewart EE75
    Jun 29, 2019 at 2:04
  • \$\begingroup\$ DO you understand a battery has huge capacitance like 10 thousand Farads at << 1 OHM and a lemon is a million times small C and higher R ?. \$\endgroup\$
    – Tony Stewart EE75
    Jun 29, 2019 at 16:38

3 Answers 3

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A lemon battery is like a small pipe with a certain pressure behind it. A dry cell is like a big pipe with a certain pressure behind it.

Putting lots of lemons in parallel is like putting lots of little pipes in parallel.

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  • \$\begingroup\$ So with this analogy the quantity of the water would decrease but wouldn’t the speed of the water increase to some extent being forced through a smaller pipe? \$\endgroup\$
    – Joseph U.
    Jun 28, 2019 at 23:26
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The statement of your question seems to indicate that you don't have firmly in mind the differences between series and parallel connected electrical components.

The voltages across components connected in series are added together. Two alkaline cells must be connected in series, not parallel if they are to produce 3 volts. The same current flows in all components connected in series.

Two resistances in series also add together. Two equal resistances connected in parallel result in half the resistance of a single resistance.

You are essentially correct about internal resistance being the reason that 3 volts obtained from lemons not being capable of producing as much current as 3 volts obtained from alkaline batteries. To completely understand what is going on, you probably need to completely understand the electrochemical process, but the end result is much like higher internal resistance in the lemons.

The water analogy is helpful up to a point, but you really need to get past that for a good understanding of electrical circuits.

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3 volts aren't an energy. It's a voltage. Electrical energy is voltage multiplied with current multiplied with time.

The lemon battery has a much higher inner resistance than the alkaline batteries. That's because the electrode surfaces are tiny in the lemon battery and huge in the alkaline batteries. They are optimized for that.

When you put a load to a battery, the load resistance and the inner resistance of the battery are in series, so they add up. Even at the same source voltage of e.g. 3 volt, the current through the load is much smaller for the lemon battery because of its higher inner resistance. In addition, the most part of the few energy provided by the source is turned into heat inside the puny lemon battery because it's inner resistance is rather high.

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