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Power source, internal resistance and Ohm's law?

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timelessbeing:

--- Quote from: Mr D on June 05, 2019, 08:16:16 pm ---Voltage is the measure of the "push" available.
--- End quote ---

Yes. Volts are a measure of Electromotive Force


Plumbing is a good analogy for electricity.
Think of water pressure as electrical potential, and the cross section (for example hose diameter) as resistance. The volume of water moving past a point is like current.


--- Quote from: Mr D on June 05, 2019, 08:16:16 pm ---But the equation for current with zero resistance is i = V / 0, which is meaningless and not even allowed in algebra?!

--- End quote ---
As resistance approaches zero, current diverges to infinity. Obviously no such thing.

AG6QR:

--- Quote from: Mr D on June 05, 2019, 07:30:37 pm ---A 1 volt battery is a very small, weak battery, right?

--- End quote ---

Not necessarily.

The voltage of a cell is determined by the chemicals involved in the reaction, not by the size of the cell.  I'm not aware of any common battery chemistries that have a 1V output, but 1.2V is certainly common, for example in rechargeable NiCads that used to be so popular.

Any NiCad cell has 1.2V, whether it's a AAA cell or a 500 pound behemoth.   Large NiCad batteries usually consist of multiple cells in series, but at least in theory, you could wire a few hundred thousand AA NiCad cells in parallel to create a single 1.2V battery.  Such a 1.2V battery would have a minuscule internal resistance and would be capable of many kiloamps.

I can't think of a practical reason to do it, but it could be done.

cur8xgo:
heres a much better way to get it in your head

voltage is equivalent to potential energy

just like lifting something in the air and asking "how much work can this thing do if I drop it?"

now to get my point across..1V may seem like not very much voltage, so cant "do" very much

by that logic, lifting something 1 inch off the ground seems like it cant "do" very much

really? how about if you lift 10,000 empire state buildings off the ground 1 inch then ask what work you can do with the energy released by dropping them?

Mr D:
Thanks, but can you clarify your analogy?

Is voltage like the weight that's going to fall one inch, or like the distance (1 inch) an arbitrary weight is going to fall?

But i like your analogy for another reason:

You asked: "how much work can this thing do if I drop it?"

If there is nothing for the weight to interact with, it'll fall forever. So it'll do an infinite amount of the least possible amount of work!?

Is that like, in an ideal circuit, the current becoming infinitely high when a voltage pushes current down a wire with no resistance?

AG6QR:
Lifting mass through a gravitational field is somewhat like "lifting" charge through an electric field.

The unit of mass is the kilogram.  The unit of charge is a Coulomb (about 6x10^18 electrons)

On earth's surface, it takes about 10 Joules to lift a 1kg mass 1 meter.  It always takes exactly 1 Joule to "lift" 1 Coulomb of charge through a 1 Volt electric field.  That's another way of saying that a Volt is one Joule per Coulomb.

An amp is the rate at which charge moves through a circuit.  An amp is one Coulomb per second.

The power equation says that power is Voltage times current. 

(Joule/Coulomb)x(Coulomb/sec) = Joule/sec

The definition of a Watt is a Joule per second, so the units do work out the way they should.

The corresponding excercise for gravity is left for whomever wants to do it.

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