Electronics > Beginners
On a 250V capacitor or a CRT, is the negative terminal -250V?
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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:

--- Quote from: soldar on May 31, 2019, 07:51:22 pm ---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.

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

--- Quote from: Starglider on May 31, 2019, 07:53:03 pm --- Cool but if I talk about elastic membranes and inductors to ten year olds it doesn't go well...
--- End quote ---

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.
 


--- Quote from: Starglider on May 31, 2019, 06:29:14 pm ---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?

--- End quote ---

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:

--- Quote from: Brumby on June 01, 2019, 12:45:56 am ---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.
 


--- Quote from: Starglider on May 31, 2019, 06:29:14 pm ---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?

--- End quote ---

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.

--- End quote ---
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?
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