Does Electronic Current Flow Like Water?

If you think about an asylum, there are two kinds of people in it: staff and patients. We aren’t sure which one [Nick Lucid] is in the latest The Science Asylum video that tries to answer the question: does electricity really flow like water?

If you think about it, that isn’t such a strange question. We talk about electrical current — just like current in a stream. Many introductory books on electricity try to relate voltage to water pressure, electric current to water flow, and resistance to changes in pipe volume. Of course, you probably figured out that analogy doesn’t — ahem — hold water to some level of detail, but just how far off is it? We won’t spoil the surprise so you can watch the video to find out, but there were several really interesting tidbits. How fast do electrons drift through a conductor? The speed of light? Actually, no — remember, drift velocity is the average speed of an individual electron, not the speed of the electric current.

So if electrons aren’t moving at the speed of light, how is it we make all kinds of circuits and antennas that rely on the speed of light? The video shows why this works, even if individual electrons don’t move nearly as fast. In fact, the speed is so slow that electrons in an AC circuit hardly move at all since they just pace back and forth a very small amount on each half cycle.

One of the things that complicates the picture compared to when many of us were in school is we now understand a lot more about the quantum nature of things at this scale and that’s always confusing. Surprisingly, the video also gives some intuition about skin effect that might come in handy.

31 thoughts on “Does Electronic Current Flow Like Water?

    1. When I was a yung ‘un I read circuits backwards because I read that current flows negative to positive. That habit proved hard to break when I got back into electronics three years ago.

      1. When I went to tech school it was still common to see tube equipment in most shops, from cosumer electronics to two way radio. Due to that ectron flow from negative to positive was well ingrained. I still revert to that when studying schematics that include solid state devices. I have no problem with changing course when working with newcomers to electric. Of course in school when we got to solid state we learned of charge carriers and such. I don’t recall hearing the word quantum, perhaps the instructors felt that would create a mass exodus of those who where still struggling with the simpler science of it all.

    2. Is this a purposely composed trick question? In modern times current flow is defined as the flow of an electric charge, so the naure of that char, and charge carriers will determine the direction of current flow. In classical ectron flow, can you falify that negative to positive direction of flow?

      1. Yes, it’s a trick question. re: show proof please! Should have been the dead giveaway. There is no proof either way. Learning the direction of flow is unimportant. Keeping one line of though in circuits is the thing. Some people point to proof of pos to neg. By pointing to lightning. Everyone can see the bolt flow down from the clouds (pos charge). And claim proof. But that’s wrong because lightning starts as weak feeler’s coming out of the ground. Which in turn meet feeler’s coming down from the cloud. The feeler’s are very faint. Only when two feeler’s meet. The big discharge come down to the ground. Every time you see crooked lightning it’s all the failed feeler’s lighting up.
        Fact of the day: Lightning strikes the earth 24/7 at roughly 100hz.

      2. “Is this a purposely composed trick question?”

        So here’s the funny part- I think the original poster is trying to get people to prove that electricity is the flow of *electrons*, meaning they flow from negative to positive. Or to try to say that there’s no real proof either way (as he stated later).

        But the problem with this is simple: he didn’t ask which way do the charge carriers flow, or which way does electricity flow. He asked which way does *current* flow.

        And current has a definition in physics, and it’s a vector – so there’s absolutely, 100% a correct answer: in a conductor, current is just the conductivity times the electric field in the medium. Which means that current direction is from positive to negative. Yes, it’s backwards from the way the charge carriers flow, but that doesn’t matter, it’s convention.

  1. “…drift velocity is the average speed of an individual electron…”

    It’s the average velocity of an individual electron, usually a couple centimeters per second if I recall correctly. The average speed is something really, really high that I can’t remember off the top of my head. The velocity is low because of the changes in direction, not because the electron is actually traveling at a low speed.

  2. Make a water hose analog of a transformer.

    Hint: it works if you make the coils out of expandable materials and place them very snugly together.

    Why? Because a static pressure difference along such a strechy hose will balloon up one end and shrink the other, acting like an analog of an inductor over some range of pressures. When the differential goes away, the hose returns to its original shape and the current continues in the same direction until the displacement evens out, modeling the self-inductance of the coil.

    Now, what happens when you intertwine two such loops of hose such that the expansion of one causes the contraction of the other? The difference in displacement transfers across the two hoses, and an “AC” current may pass through.

    1. Your analogy may be useful to explain how an AM transmitter modulator transformer works, but respectfully it fails a as an analogy for the basic simple transformer works this t fails, IMO. There has to be a moving magnetic field between conductors for one to induce current in the other. I’m unaware of any water analogy that represents how the electromagnetic field is created around a cunductor that has current flowing through it.

      1. The expansion of the stretchy hose models the energy stored in the magnetic field, and its displacement gets transmitted to the adjacent hose, causing the water in that hose to squeeze towards the other end.

  3. Just to muddy the waters with a bit of conflation .. current flow in water is a very strange animal. The double-layer effect and a number of other quirky charge effects are readily observable with any ordinary multimeter.

    Jist for fun, put some water in a glass, and add a bitnof salt. Put two spoons in and measure the resistance. Once that bexomes boring. Swap the electrodes. Once that becomes boring, measure the voltage .. etc. Then try something similar with, say, leads for mechanical pencils.

  4. If my kids are spending too much time in the shower and I need to cut them off, I can close a valve and stop the flow instantly. The effect propagates down the pipes much faster than the water ever moved. When it comes to signal propagation in a wire, electricity is more like a shock-wave going through a pipe. When it comes to powering LED’s its more like a fluid. Of course electricity is what it is with no regard to how well it matches to ideas we try to model it with like “shock-wave” or “fluid”. It’s perfectly happy to be different…similar…itself. :-)﻿

  5. When I was a kid, I had an elektor kit. They used water analogies to explain electronic component… For resistors, capacitors, diodes, transistors, but also for tension and current… Worked rather good if you ask me…

  6. I definitely think that electric current flows like water, and in fact that electric current is probably involves many particle collisions in the process as the stream plows through other matter. One interesting point is that in the 1700s the theory that electricity is made of two opposite moving streams of fluid was published- Ben Franklin then put forward a single fluid theory, but over the course of many years I think the two fluid theory can’t be ruled out in some instances, like in electroplating- how else to explain how both anode and cathode coated if not by two opposite moving streams of ions?

    1. adding that in my humble opinion most of modern day science, certainly physics, astronomy, and famous crimes are total and unadulterated bunk- somehow mysteriously biology, math, and chemistry have mostly escaped the outlandish fraud.

      1. I modeled a long pipeline as an electric circuit for purposes of leak detection back in the 1980s. The trick is, the “resistance” of the pipe varies based on the Renolds number which tells you how laminar the flow is. Non laminar flow produces higher resistance values, so you can’t just calculate R and you are done. The pipe is a variable resistor. But if you can do that math correctly, the results are pretty good. Essentially the pipe is a big resistor. You measure flow and pressure at one end and flow at the other end. A leak looks like an extra resistor to ground, somewhere in the middle of the resistor.

Leave a Reply to Doug Cancel reply

