On a 250V capacitor or a CRT, is the negative terminal -250V?

[soldar]

In a  hydraulic model a capacitor would be a chamber with pipes on opposite sides and an elastic membrane separating both halves. The more water you pump from  one  side to  the other the more pressure  you need.

A long pipe is an inductor.Etc.

[Starglider]

In a  hydraulic model a capacitor would be a chamber with pipes on opposite sides and an elastic membrane separating both halves. The more water you pump from  one  side to  the other the more pressure  you need.

A long pipe is an inductor.Etc.

Cool but if I talk about elastic membranes and inductors to ten year olds it doesn't go well...

[soldar]

Cool but if I talk about elastic membranes and inductors to ten year olds it doesn't go well...

In that case I can't see how talking about capacitors or voltages makes any sense. The water model is as intuitive as you  can get.

[Brumby]

As I said before, all analogies have problems - and the water one does too, BUT it is helpful in getting some initial concepts across.  Also - water being incompressible is not a problem at all.  This detail is, in fact, more "correct" than the gas analogy.
 

Would you guys say the simplified layman's explanation given at 4 minutes into this video is a good one for giving a basic understanding to non engineers? https://youtu.be/a6FMpvs71pc The video owns that it is a simplified explanation.

The energy being converted into the light and heat of a spark, so going into the atmosphere and therefore not needing to go into a ground cable? Makes sense but is it correct?

Yes.  That video from 4:05 to 7:00 explains it pretty well.


While we're on the subject - let's straighten something out ... What is "ground" or "earth" as far as electronic circuits are concerned...?

OK - Let's assume you've made up a circuit on a breadboard, running off a battery.  Now, get a piece of wire (of any length - but let's use a piece 1 foot long) and lay this on the bench top about 6 inches from the breadboard. 
 >>> Does this extra wire have any effect on the circuit?  No.  Does the circuit still work?  Yes.
Now connect one end of this wire to one point of the circuit on the breadboard.
 >>> Has anything changed?  No.  You have not made a path for electrons to go anywhere.
Remember, this path must be in the form of a loop.  No loop = no electron flow!

As far as the electrons are concerned, this extra wire is your "ground" or "earth".  For a battery powered circuit, it works exactly the same way as if you had a stake driven into the soil with the wire attached to it.  That is, it will do nothing!

In fact, this is true for any circuit which is powered by an isolated power supply.


Where the "ground" or "earth" connection does come into play is where there is more than one connection to it from different points of a circuit.  Mains power is the most common example - and is the source of the magical, mysterious and sometimes reverent esteem held for the connection called "ground" (or earth).

But there's nothing mystical about it at all - other than the fact that it is not obvious to your average householder....

The bit that is important in the dashed line that runs through the soil, the metal stakes at each end and how that all forms part of a circuit - and you see how there is a loop!

It is because of this arrangement that you will get a shock if you touch a mains "active" and something that is grounded (connected to the soil).  You just added another loop path.

IF that earth connection at the substation (or pole transformer more usually) were not in place, you could grab onto a mains active and touch as many earthed things as you like - and you would not get a shock.  (Such a condition would be far more dangerous, actually.  It would allow anyone connected to the mains supply to have a fault that could put 10,000V on that wiring which does have an earth connection - and then your shock risk is a lot more.)

[Starglider]

As I said before, all analogies have problems - and the water one does too, BUT it is helpful in getting some initial concepts across.  Also - water being incompressible is not a problem at all.  This detail is, in fact, more "correct" than the gas analogy.
 

Would you guys say the simplified layman's explanation given at 4 minutes into this video is a good one for giving a basic understanding to non engineers? https://youtu.be/a6FMpvs71pc The video owns that it is a simplified explanation.

The energy being converted into the light and heat of a spark, so going into the atmosphere and therefore not needing to go into a ground cable? Makes sense but is it correct?

Yes.  That video from 4:05 to 7:00 explains it pretty well.


While we're on the subject - let's straighten something out ... What is "ground" or "earth" as far as electronic circuits are concerned...?

OK - Let's assume you've made up a circuit on a breadboard, running off a battery.  Now, get a piece of wire (of any length - but let's use a piece 1 foot long) and lay this on the bench top about 6 inches from the breadboard. 
 >>> Does this extra wire have any effect on the circuit?  No.  Does the circuit still work?  Yes.
Now connect one end of this wire to one point of the circuit on the breadboard.
 >>> Has anything changed?  No.  You have not made a path for electrons to go anywhere.
Remember, this path must be in the form of a loop.  No loop = no electron flow!

As far as the electrons are concerned, this extra wire is your "ground" or "earth".  For a battery powered circuit, it works exactly the same way as if you had a stake driven into the soil with the wire attached to it.  That is, it will do nothing!

In fact, this is true for any circuit which is powered by an isolated power supply.


Where the "ground" or "earth" connection does come into play is where there is more than one connection to it from different points of a circuit.  Mains power is the most common example - and is the source of the magical, mysterious and sometimes reverent esteem held for the connection called "ground" (or earth).

But there's nothing mystical about it at all - other than the fact that it is not obvious to your average householder....

The bit that is important in the dashed line that runs through the soil, the metal stakes at each end and how that all forms part of a circuit - and you see how there is a loop!

It is because of this arrangement that you will get a shock if you touch a mains "active" and something that is grounded (connected to the soil).  You just added another loop path.

Glad you like the video!

Good ground explanation that thank you. isn't it true that the ground cable on mains power outlets only came about as a safety precaution so that manufacturers could wire their metal parts to the ground instead of to the live as they used to, thus reducing fatalities?

[Brumby]

Good ground explanation that thank you. isn't it true that the ground cable on mains power outlets only came about as a safety precaution so that manufacturers could wire their metal parts to the ground instead of to the live as they used to, thus reducing fatalities?

That is my understanding.  By having grounded metal bits connected to earth, any internal failure that caused the mains live to come into contact with any of those metal bits (like the case) would find a path through the earth wire - and not through a person.

In the above example, a keen observer might ask - Wouldn't connecting such metal bits to the neutral do the same thing?  The answer to that is "Yes, but".  The "but" is that you would need to guarantee that you could depend on the neutral connection being the actual neutral - and in the case of non polarised mains plugs, this is just not possible.  Even in the case of polarised systems, such as we have in Australia, you could have a mains socket, extension lead, etc. wired up incorrectly - and as far as swapping the active and neutral is concerned, the appliance couldn't care less and will work happily.

[ArthurDent]

This site has some good short explanations of capacitors (and other thingies)

https://www.khanacademy.org/science/physics/circuits-topic/circuits-with-capacitors/v/capacitors-and-capacitance

[radiolistener]

Also - water being incompressible is not a problem at all.  This detail is, in fact, more "correct" than the gas analogy.

For electric current in the metals, where charge is carried by electrons, gas model is more correct and is really used for modeling.

About water model I'm not sure, may it can be accepted to explain electric current in electrolyte, where charge is carried by ions instead of electrons.

[Brumby]

Maybe we are talking at crossed purposes here...

My approach has been one directed at helping a 10 year-old grasp some basics, not define a computer modelling framework for real world simulation.

My way was meant to be obvious - even if not perfectly correct.
Yours might be correct, but it is not as obvious.

... to a 10 year-old.


The success of an analogy will be demonstrated when the student starts asking questions that show they are seeing the shortcomings.

[james_s]

No analogy is perfect, electricity is neither a liquid nor a gas. Water generally makes a good analogy though to understand basic concepts. Everyone has handled water, you can see water, you can feel water, it's universally available, everyone knows how water behaves. The analogy doesn't always work but it's usually a good place to start.