Hello Cyril Mechkov,

Your attached "riddle" is a nice analogy to constant-voltage capacitor charging through a series resistor. I think, it would have been better if the rightmost tube were drawn longer to assure that water will not spill out when its level tends to attain the same height as in the left tube.

I appreciate your approach of explaining electrical circuits through non-electrical analogies. They are sometimes a good way to introduce a new concept through a familiar one. But don't you think that there is a risk that this may introduce misconceptions? For example, the analogies of water, pipes, filling tanks work for electrical circuits as basically both the Coulomb and the gravitational forces vary with distance as 1/r^2. But there are important differences, like masses never repel each other, but charges of the same polarity do. Also, using the water-in-pipes scheme how do you differentiate among a resistor, a capacitor and an inductor?

My opinion is that earlier the learner thinks 'electrically' about electrical circuits is better. May be, I'm missing a point.

Hi, Kanad!

Thank you for the reaction of my "philosophical" circuit question and for the answer to the circuit puzzle in the attachment. The "constant-voltage capacitor charging through a series resistor" sounds very intriguing for me...

Yes, in this clever circus trick of a "bottomless vessel", the water level of the right vessel (the voltage across the capacitor) stays constantly zero although we continually fill (charge) the vessel (capacitor). About your trouble that "the water in the rightmost tube will spill out when its level tends to attain the same height as in the left tube", I will add another trouble - that first the bottom of the vessel will touch the ground-:) It is still interesting to say the name of this clever circuit and the basic idea behind it. It is extremely interesting to see how "the water will spill out" and "the bottom of the vessel will touch the ground" in the electrical circuit. I have placed the imperfect version of this circuit in the attachment below to help the answer...

Yes, "it is a good way to introduce a new concept through a familiar one"; I will add that this is just obligatory in teaching. The analogies play here the only auxuliary role; so, they shouldn't be applied strictly. They have to be a kind of generalized analogies...

BTW the communicating vessels is a quite happy analogy of this electrical circuit. The water level H corresponds to the voltage V, the water volume - to the charge Q, the bottom area S - to the capacitance C, the water flow - to the current I, the pipe constraint - to the resistance R. The vessel acting as a voltage source is extremely wide (or someone keeps a constant water level)...

What do you think about my non-electrical explanation how the AC current "flows" through a capacitor? Here is the question:

https://www.researchgate.net/post/Does_the_current_flow_through_a_capacitor_and_if_so_why (see the last comment)

Regards, Cyril.

Hi Cyril,

You are saying that "the water level of the right vessel (the voltage across the capacitor) stays constantly zero although we continually fill (charge) the vessel (capacitor)".

That is not correct as long as the water in the vessels are continuous (interconnected), no matter how constricted the connecting path between them is. This is a very simple hydrostatic principle on which syphons work. You can do a simple experiment to see for yourself.

The voltages across the capacitors in the associated pictures will eventually rise up to the respective battery potentials: (E+Ec) in the first picture, and E in the second picture. The resistances in the circuits will determine the rates at which the capacitors will be charged (through the RC time constant). Similarly, the constriction in the interconnections of the vessels will detemine how quickly the heights in the columns are aligned.

Kanad, notice that "the water level of the right vessel (the voltage across the capacitor) stays constantly zero" but regarding to the ground, not to the bottom of the right vessel...

I agree with you that "voltages across the capacitors in the associated pictures will eventually rise up to the respective battery potentials: (E+Ec) in the first picture, and E in the second picture"... but I would like to ask you if you have noticed the man in the ditch; his role is crucial in the first arrangement above. When my students and I mentally carry out this sophisticated experiment in the classroom and then really in the laboratory (the small phone picture below from 2004), I usually do this "donkey work"-:) After I get bored, I assign this task to a humble op-amp and it perfectly continues doing it...

Thank you for the contribution. Regards, Cyril.

Prof.Cyril,

I am elated by the confidence and trust placed by you on me in associating me with a question.Due to pressure of Academic Work I could not respond immediately though I saw your Riddle. I apologize.

As I mentioned earlier there is a school of thought that there is only one Engineering called "Systems Engineering" and that any problem in any system can be solved with proper mathematical equations.Redefine the variables and boundary conditions,the problem in one system can give proper solution to the one in any other system.

Hence by drawing and solving equivalent analog circuit for a problem in any other field we can get the solution for that problem.

But, this is for persons with knowledge in Circuits.

But, for a novice in circuits which is abstract and not clear,as you rightly said analogy from known physically visible examples,understanding of the behavior of the electronic / Electrical circuits can be made easy.

This is amply demonstrated by your yeoman service on Circuit Fantasia.

I agree with your summarisation of the explanations for the two figures. The discussions of Prof. Kanad Mallik are quite interesting.

As pointed out physical examples can be taken only up to some level and not to extreme end.

By the bye, the figures can also explain the simple fundamental Ohm's law regarding current flow.

Dr.P.S.

Dear colleagues,

allow me to share in your discussion about to understand a circuit. Cyril raised a very important point about the the role of the teacher to introduce the subject of the electrical and electronic circuits to the college students.

For the student to understand the electrical circuit he must before understand well the basic principles of the electrical engineering as a prerequisite. HE must be aware of the electric charges, their interaction, the electric fields,the potential energy, the sources of electricity,the electric current and its effects especially the magnetic effects. The behavior of the electrical elements and so on. Understanding the electricity and its behavior and effects and the familiarity with it is very important for grasping the electrical circuits In these primary courses on electricity the analogy with nonelectrical quantities may be helpful for resolving the electrical quantity provided that the nonelectrical quantities are well known and well understood for the students. Analogy between fluids and electricity is justified when only the teacher sees its usefulness to the students. May be equally helpful to intensify the use of the laboratory to make the students familiar with the electrical quantities.When the student measures the voltage the current, the power,..etc many times and deals with the elements and components he will be able explain their performance in his own words and he will be able to apply them in new applications.

I agree with you that the professor must prepare the course stressing the basic principles and the big ideas behind the circuits. For example, before he treats the different oscillator circuit he must introduce the oscillator theory and then introduces the different oscillator circuit as an application on the theory.

Thank you Cyril for invoking this important question.

Here is the answer of the "circuit riddle"-:)

http://en.wikibooks.org/wiki/Circuit_Idea/Voltage_Compensation

http://en.wikibooks.org/wiki/Talk:Circuit_Idea/Voltage_Compensation

Regards, Cyril.

Splendid idea.

It is the same old mystic topic of Virtual Ground at the inverting terminal of Op_amp with negative Feed Back, about which we had been discussing a lot tirelessly.Only thing is that we have a capacitance and not a resistance in the feed back path,an Integrator.

Without thinking about the Op_amp we had been discussing only about normal circuit ideas for this riddle.

Thanks a lot, Professor for indirectly suggesting not to view in only one angle but to Widen our Horizon.

Dr.P.S.

Yes, Pisupati... yes... this is the same great "virtual ground" idea... Only I would say that "voltage compensation" is the great idea and the virtual ground is only the result of this (successful) voltage compensation; it is an indication of the equilibrium. And I would add that we will see the virtual ground if we have a real ground. But if we have not a real ground? Then we have to talk about a "virtual zero voltage" between two points...

I am glad to see you again and I am thankful to you for your warm-hearted contributions... they have moved me... I know all we miss Lutz as well and all we are waiting for his return here, to our team. I hope he, even been far away, keeps an eye open, from time to time, for our discussions... Thank you, my friend, again...

Best regards, Cyril

Dear Cyril,

You are quite correct as electrical circuits are simply a subset of other basic or general laws of physics and as such one may draw powerful parallels or analogies to other systems.

Your adapted second example is a simple but powerful demonstration of the transfer of energy from a source to a load. In the case of the electrical circuit energy is transferred from the source (potential energy stored in electric field) via the transfer of electric charge (kinetic energy stored in the magnetic field) and stored in the capacitor (potential energy stored in electric field) and the energy lost during transfer is represented by the (heat) dissipated in the resistor. What is not so obvious is that regardless of R the energy required or lost is always half of the energy transferred and leads to the concept of displacement current.

If as Abdelhalim points out we note that R,L&C are man made constructs used to represent energy lost as heat (R), energy stored in the magnetic field (L) and energy stored in the electric field (C) then the analogies become more powerful.

Whilst the analogy used is correct in terms of energy in general the one utilises electromagnetic fields for the transfer of energy whereas the other uses the gravitational field. These fields are quite different (macro vs micro) from a physics definition or viewpoint but interestingly they behave the same.

Both circuits prior to energy transfer are static potential fields which become dynamic during the energy transfer and which become static once energy transfer has occurred and a steady state energy balance achieved. This shows accordance with Newtons laws for both circuits and parallels that of EM theory for static EM fields.

However an important difference is that the electric system in the example requires a closed circuit for the transfer of energy whereas the water tanks are an open circuit. This implies energy may be transferred via or within an open circuit and which was discovered as propagating EM waves.

The example shows how the generalised properties of fields may be exploited to our benefit in that any difference created in or by a field may be used to make it do work. Of course work has to be done to store energy and create fields but once done they will automatically do work and further may be controlled to our benefit.

Using this knowledge and exploiting the properties of materials are the fundamentals of engineering as to how we can best exploit science (and technology) to our benefit.

Signals at the Transmitter and the Receiver are no doubt earthed completing the circuit, Only thing is that both Electric and associated Magnetic Waves are transmitted through Space.

Just like the return current through Ground wire or Ground are there Return EM waves through Ground?

Just as we consider Image Conductors in Transmission lines to make the Electric or Magnetic fields at Ground to be zero do we have to consider Image waves at equal depth below the Ground(equal to height )?

Or similar to the Corpuscular and wave theory of light should we consider charge flow and electric Field Radiation and associated Magnetic Field or Waves?

I am posing this as a separate question on the original topic of,"What does "to understand a circuit" mean? " posed by Prof Cyril.

P.S.

Well I suppose sending a message from one cell phone which is not earthed to another cell phone which is not earthed appears to answer this. Possibly not much different to sunlight warming us up. It alludes to energy being stored / contained in the propagating EM waves / fields.

However, Tesla is said to have exploited or tapped the electrical energy in and between the ion-sphere and earth through a huge resonant circuit back in the 1880's.