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Veritasium "How Electricity Actually Works"

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PlainName:

--- Quote ---And the word trough means something completely different than in / out.
--- End quote ---

Suppose you have a pipe with a diaphragm separating the left from right sides, both filled with water. A piston on the left side is pushed in, and as a consequence a piston on the right is pushed out.

Water is pushed in, but no water transfers from left water to right water. However there is energy transfer through from one piston to the other.

electrodacus:

--- Quote from: dunkemhigh on May 20, 2022, 12:09:45 am ---
--- Quote ---And the word trough means something completely different than in / out.
--- End quote ---

Suppose you have a pipe with a diaphragm separating the left from right sides, both filled with water. A piston on the left side is pushed in, and as a consequence a piston on the right is pushed out.

Water is pushed in, but no water transfers from left water to right water. However there is energy transfer through from one piston to the other.

--- End quote ---

That is a bad example.
I already provided a better example but as any analogy will still have limitations.
A cylinder separated with a diaphragm but filled with air or any other gas.
If pressure is equal on both side it will be equivalent to a discharged capacitor so there is no stored energy.
You can install a pump that takes air molecules from one side and moves them in to the other side.
Say you start with 1000 molecules on each side so 2000 molecules in total.  Then you use the pump so you need to put in some mechanical energy to push air from one side in to the other side charging this energy storage device with energy.
Say you move 500 air molecules from one side to the other so now you have 500 on one side and 1500 on the other.
Now say you want to charge an identical discharged cylinder from this charged one.
You will connect two hoses (hoses also have air in them just at normal pressure) so when you connect to the discharged cylinder
pressure will want to equalize.
You start with an excess of 500 air molecules one one side and a deficit of 500 molecules on the other side so 250 molecules will be transferred for the pressure to equalize.
You end up with 1250 / 750 in both cylinders. So was there any work done other than the heat loss due to friction of moving the molecules from one cylinder to another ?

But as mentioned you can not push any analogy to far.

IanB:

--- Quote from: electrodacus on May 19, 2022, 11:47:42 pm ---Energy stored in capacitor is not work.
--- End quote ---

Work has to be done to store energy in a capacitor. So the energy stored in a capacitor results from the electricity doing work.

There is either heat or work. If the electricity is not generating heat then it is doing work. If it is not doing work then it is generating heat.


--- Quote ---So in my example capacitor stored 72mJ so half of what the source provided the other half was converted in to heat.
--- End quote ---

Half of what the source provided was used to do work on the capacitor, the other half was converted to heat.

electrodacus:

--- Quote from: IanB on May 20, 2022, 01:08:33 am ---Work has to be done to store energy in a capacitor. So the energy stored in a capacitor results from the electricity doing work.

There is either heat or work. If the electricity is not generating heat then it is doing work. If it is not doing work then it is generating heat.


Half of what the source provided was used to do work on the capacitor, the other half was converted to heat.

--- End quote ---


You are confusing work with stored energy.
In fact you completely ignore energy storage as if it was not still there.
Out of the 144mJ of energy from the supply half was converted to heat the other half was stored in the same form that it was delivered so electrical energy.
That other half is stored in the capacitor and you can do whatever you want with it as it was not been used to do any work.

Not sure why is so hard to get that energy is in the same form electrical energy and it is available it was not used.
The capacitor is now a source containing 72mJ.


I think you accused me of violating the energy conservation but it looks like that is you.
I say 144mJ delivered by source = 72mJ as heat in the wires + 72mJ stored as electrical energy.
You say 144mJ = 72mJ as heat in the wires + 72mJ work + 72mJ stored ???

IanB:

--- Quote from: electrodacus on May 20, 2022, 01:40:20 am ---I think you accused me of violating the energy conservation but it looks like that is you.
I say 144mJ delivered by source = 72mJ as heat in the wires + 72mJ stored as electrical energy.
You say 144mJ = 72mJ as heat in the wires + 72mJ work + 72mJ stored ???

--- End quote ---

You didn't read what I said. You must learn to read.

Energy = Heat + Work

144 mJ (Energy) = 72 mJ (Heat) + 72 mJ (Work)

It's not complicated, is it?

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