Electronics > Beginners

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

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Brumby:

--- Quote from: Starglider on June 01, 2019, 12:52:20 am ---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?

--- End quote ---

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:

--- Quote from: Brumby on June 01, 2019, 12:45:56 am ---Also - water being incompressible is not a problem at all.  This detail is, in fact, more "correct" than the gas analogy.

--- End quote ---

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.

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