DC Circuit Water Analogy (1998)
hyperphysics.phy-astr.gsu.edu
hyperphysics.phy-astr.gsu.edu
Click on the 'Circuits' menu to see dozens of example circuits.
One issue with the hydraulic/fluid analogy is the "empty pipe" misconception - we forget or don't know that in electrical circuits, the circuit is a closed loop. An example of this misconception is that beginners sometimes think the current "wears out" as it goes along the wire. The Falstad simulation shows a line of moving dots that move faster or slower depending on the current - a little more like a train moving in a pipe - which helps counter this misconception, although it, too, isn't perfect. As a next level, I like showing animations/simulations that show the role of charge on the 'outside' of the wire in steering current flow, as well as magnetic fields surrounding the wire.
Open circuits work fine if there is a powerful source of electricity (like a a radio) and a sink (like the Earth), and same for water (an icy comet crashing into a cliff, making a waterfall).
An open water circuit is full of stationary water.
Here are math and physics ones: https://falstad.com/mathphysics.html
I like the 2D vector field one https://falstad.com/vector (2d) and the 3d one https://falstad.com/vector3d.
Antenna simulator: https://falstad.com/antenna
Waveguide is awesome too https://falstad.com/embox/guide.html. Don't forget to pick various modes in the little square at the bottom.
If Paul Falstad comes around these parts, thank you for creating and sharing those!
Did you know - a boost switching regulator was used to pump water up to the top of a garden in Victorian times. The regulator uses the water pipe analogy to electricity, except electricity hadn't really been invented then. The system uses an inductor (a long straight pipe, where the water has momentum), and a switch (a flap that closes and opens regularly), with a diode (one-way valve) and a capacitor (a container with a pressurised air cavity). https://en.wikipedia.org/wiki/Hydraulic_ram
https://www.kickstarter.com/projects/upperstory/spintronics-...
My 9 year old brother found it quickly too hard though.
It does a good job of introducing concepts slowly but they are in fact hard concepts if you're new to them. It is actually a bit of a challenge for adults too.
Mechanically, the game is good but a bit finicky to set each piece in place. That means the time between "I think I know what to do" and testing it out is a bit too long. Overall, I find it pretty fun though. (I also backed the spintronics kickstarter)
How would you model mutual inductance in other circuits?
Helmholtz resonators[1] are used to provide capacitive acoustic impedance in a gas system. Archetypically a beautiful hollow copper sphere. Ported subwoofers use the same formulas, as do some types of automotive exhaust. Exhausts use a long pipe and cylindrical section to form a low-pass filter, which transforms the individual exhaust bursts of an engine into a smooth continuous flow. Two stroke exhausts[2] are band-pass filters that improve compression by putting backpressure on the engine at the correct time.
[1]: https://en.wikipedia.org/wiki/Helmholtz_resonance
[2]: https://en.wikipedia.org/wiki/Expansion_chamber#/media/File:...
https://acousticstoday.org/past-issues/james-clerk-maxwell-a...
It led to many EEs getting a certificate in fluid & thermo because the extra couple classes counted as tech electives and the math was the same.
I would love to find a book with this type of presentation. Do you happen to remember which textbooks were used for this class?
SchÖnfeld, J. C. (1954). Analogy of hydraulic, mechanical, acoustic and electric systems. Applied Scientific Research, Section B, 3(1), 417–450. doi:10.1007/bf02919918
Still, I think the water analogy is over used
I mean, it’s probably worth mentioning current and voltage are “kind of” like flow, pressure etc., in a first lecture to start to get the basic idea, but then warning not to think of it as being the exactly same because that will just be confusing later.
The water analogy, is, in my opinion, the sweet spot for people who will never own a multimeter or fire up a SPICE program. It's the level that ought to be the expectation for citizens of a technic civilization.
What you can't do is design a bottom dollar power supply that uses some trick circuitry to not emit enough RF noise to matter.
All radio/wifi and everything involving fiber optics or magnets. That's probably slightly more than 00.001% of applications.
It's just as easy to understand without need for analogies.
Based on what you've described, where would you develop the intuition about the difference in speed between the electrons and the electromotive force they are relaying? Or why you need both voltage and current to do work, or the behavior of an LCR circuit? Or an open circuit? Etc etc.
If only! My apartment was recently destroyed by water that refused to do exactly that...
Electricity also doesn't freeze solid, expand, and break open its insulation; it doesn't evaporate and condense on cold surfaces and cling there under surface tension, it doesn't drip down.
But the analogy is still a pretty useful one for people who have lots of hands-on experience with water and not much with electricity, or vise-versa.
>> expand, and break open its insulation = an arc causes by too much electricity in too thin a pipe.
>> it doesn't evaporate and condense on cold surfaces = electro vapor deposition aka physical vapor deposition
Arcing (or shorting in general) would probably be more akin to water's tendency to find the lowest point.
[0]https://en.wikipedia.org/wiki/Injector#/media/File:Ejector_o...
If that were the case I wouldn't be paying twelve hundred bucks and counting to fix the plumbing in my mom's house.
You don't even need fancy things like transformers for energy not in the wires to be important. Even a simple DC circuit consisting of a battery in series with a light bulb mostly involves an electromagnetic field to transfer energy from the battery to the light bulb, which mostly takes place outside the wires.
The function of the wires when it comes to energy transfer is to carry moving charge which creates the magnetic part of the electromagnetic field that actually carries the transferred energy.
Here's a pretty good explanation [1]. That video was from January 2019, and not controversial. Veritasium did a video on the topic in late 2021 that didn't really present things as well and ended up being quite controversial [2]. Other well-known YouTube channels such as EEVblog [3] and ElectroBOOM [4] responded.
There was also someone who bought a bunch of wire and did the experiment as described in the Veritasium video (although scaled down). That was discussed on HN and that discussion contains some very interesting links [5].
In particular the link to a talk by Rick Hartley in this subthread is very informative [6]. He talks about how most EMI problems in PCB designs are due to people not taking into account the the energy is not in the wires.
[1] https://www.youtube.com/watch?v=C7tQJ42nGno
[2] https://www.youtube.com/watch?v=bHIhgxav9LY
[3] https://www.youtube.com/watch?v=VQsoG45Y_00
[4] https://www.youtube.com/watch?v=iph500cPK28
The right way to think about this if you _really_ care is a bit like the way that RF engineers think about dielectric resonators. The metal motivates the fields to be guided along pairs of conductors by the motion of charge carriers within. A metal will respond in a particular way to fields, which results in new fields, and so on and so forth in a way that results in the fields propagating along in a particular way.
A propagating pulse is a bit hard to think about but you can imagine some field configuration that results in the electrons in the metal slipping a bit, and those electrons move in a way that results in new fields which contain the new wavefront of the pulse. The electrons don't keep moving -- they move on average the distance of the mean free path and give their energy to the lattice as heat. This is why the drift velocity is just a meaningless number. The fields propagate at around c and the conductors guide them.
The pedagogical failure of this analogy is how it suggests that the energy is stored in the potential and kinetic energy of the fluid (the electron density) rather than in the fields. Then you end up with this drift velocity nonsense which is essentially a holdover from the Drude model which is only predictive by luck.
Pipes almost always end up having turbulent flow inside, in which case, pressure drop is proportional to flow rate squared. Whereas for electricity, voltage drop is always proportional to current. This leads to problems when trying to use circuit analogies when trying to solve for pressure drop in a system of pipes.
The water metaphor works fine for many DC circuit comparisons, up to and including basic transistor operation. Meanwhile, at AC, your statement above doesn't hold up much better than the water analogy would. Lots of additional terms come into play... skin effect, radiative losses, displacement current and phasor relationships, even quantum effects.
Every once in a while, a huge Internet argument springs up among people who don't understand that the Ohm and Kirchoff laws represent the steady-state map and not the time-variant territory. Do a search on eevblog for "Lewin," for instance. (Actually that's terrible advice. Don't do that, and forget I said anything.)
That's how modelling works.
What i find even more interesting, is that those analogies are no lucky coincidence. The rules of dynamical systems apply on a higher level. The differential equations governing those systems do not care, how the concepts of inertia, capacitance or resistance are realised in a real world system. Those are implementation details. Neither do physical principles, like the principle of least action, which 'govern' those differential equations.
*Fun fact: Classical thermals systems do not have an inductive element. That's why there are no oscillations in thermal systems. You need two kinds of energy storage for that, so that the energy can switch between them.
I looked at the photo and the description and suddenly realized I was looking at a XOR’d MOSFET low side switch circuit made of pipes and valves.
Funny that sometimes the water analogy also works the other way around.
The opposite is also true; if the flow out of a pump is blocked then the pressure will immediately climb extremely high and usually break things. Once you get into the weeds with transistors etc you obviously also have to worry a lot more about currents, but with hydraulics it's always about the flow.
Anyway.
The water analogy is pretty good, but it's important to not get too wrapped up in it. In some very fundamental ways, electricity is not like water, and believing it is will trip you up when you get into more complicated circuits or try to take what you've learned about DC and apply it to alternating current. It's a great place to start though.
After getting one's head wrapped around those, I found that Kirchoff's loop and junction rules were great, because they make intuitive sense (junction because matter is not created or destroyed, and loop because the value of a thing has to be equal to itself, so no matter what path you take around the circuit, when you return to a point of origin it must be true that the point of origin has the same voltage at the end of the path as it did at the beginning).
I guess a transistor is a little man twiddling a valve according to a dial in the "water model" of electricity, any through-space effects are due to leaks, and nonlinear components like MOSFETs are a bit more creatively explained. (E.g. Source: water reservoir; drain: water reservoir; gate: gate between source and drain reservoirs, driven by an utterly mad person who follows interesting rules. Oh, and inexplicably he's a bit stronger than transistor man too).
If you're an educator please reconsider using these analogies that fall apart later on becuase in more complex concepts but the analogy may stick on in your students head when it doesn't apply. Or at least heavily stress that these are analogies and not to expect that this "water circuit" analogy will hold forever.
behold! the MONIAC
https://www.rbnz.govt.nz/research-and-publications/videos/ma...
I recently got into electronics/electricity and I have been trying to put together a course for myself, mostly for the kind of work that involves fixing things (power supplies, small house appliances, and so on) but also for having a good understanding for how things work. Of course the field is huge and there’s all sorts of applications out there. I’m a long time software dev and I’ve delved into all sorts of software-oriented subjects over the years, so I’m hoping I can apply some of this knowledge, at least from a troubleshooting/analysis perspective. But oh boy is this difficult due to electromagnetism and not being able to really visualize these things (not without an oscilloscope I suppose).
A close family member was an EE/technician and they ran a repair service for appliances for many decades - anything and everything, TVs, radios, kitchen appliances, industrial machinery, and so on. Sadly they passed away and I don’t know anyone personally I can ask about where to begin and how to approach this.
Any recommendations for curriculum? I started with Make: Electronics 3rd Ed and a half dozen or so online resources, like the Khan Academy series and some other undergraduate level videos on circuit analysis and such. I really like the electricity misconceptions site as well.
On the other hand, the underlying theory is very useful for if you do encounter something off code, because something off code will be doing something, and you as the homeowner are stuck figuring out what.
An inductor would be something like a propeller/impeller attached to a flywheel.