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For the longest time I chose to ignore the true definition of voltage because it did not make sense to me to think of voltage by its definition. Most of the time, it made more intuitive sense to think of voltage as pressure or as a force, but these substitutions only go so far, and I'm trying to wrestle with how voltage's true definition (from hyperphysics) - "the work which would have to be done, per unit charge, against the electric field to move the charge from A to B" - makes sense when trying to understand the behavior of circuits.

Also, from what I understand you can have voltage without current but not current without voltage.

So lets say:

  • we have a voltage 'V' applied cross some point 'A' to some point 'B' then to some point 'C'
  • no current flows from A -> B -> C.
  • 'V' drops across A -> B, however the voltage at/"entering" 'B' is not 0, lets say its V - 1.

Now, say that 'B' has a input voltage tolerance of V - 2, so in this current state, 'B' is experiencing +1V more than it can accept.


My question is:

if voltage is the amount of work needed to move a charge from A -> B not the actual the amount of work being spent across A -> B but the work needed [if] we were to move a charge from A -> B

In this situation, if it takes V - 1 volts to move a charge from B -> C, but we are not moving any charge since there is no current, is the input 'B' still damaged?


If yes, why? voltage is not a force or pressure, from what it seems, its a hypothetical, its only if we are moving a charge and in this example we are not, so no physical, for lack of a better word, thing is being experienced at 'B'.

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  • \$\begingroup\$ Place yourself in a vacuum. Imagine two plates separated by any arbitrary distance (it doesn't matter.) Make one plate positive with respect to the other plate. Now you place exactly one Coulomb of charge (lots of electrons) at the more negative plate. This negatively charged Coulomb worth of electrons will be attracted to the positive plate and repelled away from the negative plate. They will accelerate and then impact the positive plate. If you can measure the heat energy of that impact in Joules, then you have the Volts that must have been presented between the plates. \$\endgroup\$ – jonk Oct 18 '19 at 6:35
  • \$\begingroup\$ @jonk I do not understand how or if your comment either is parallel to, answers, or contests my hypothetical? \$\endgroup\$ – Ietpt123 Oct 18 '19 at 6:38
  • \$\begingroup\$ @MituRaj I'm not asking what voltage is, I'm questioning the definition of voltage with a corner case hypothetical to get more insight about its definition \$\endgroup\$ – Ietpt123 Oct 18 '19 at 6:55
  • \$\begingroup\$ @letpt I was confused about voltage until the moment I read about the case in a vacuum. It cleared many cobwebs for me, in less than a second's time when I thought about it in that context. Just as Galileo's realizations from rolling balls down inclined planes led him to realize, absent friction, a ball set in motion would never stop moving. Idealized situations help clear out the mental barriers. If not for you, I'm sorry to have bothered you and we'll leave it there. \$\endgroup\$ – jonk Oct 18 '19 at 7:24
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    \$\begingroup\$ It is quite possible to have current without voltage - superconductors \$\endgroup\$ – Dirk Bruere Oct 18 '19 at 8:00
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When you state:

if voltage is the amount of work needed to move a charge from A -> B not the actual the amount of work being spent across A -> B but the work needed [if] we were to move a charge from A -> B

"Amount of work" is referring to energy. As you said on your post, Voltage is not an energy, energy would be described as Wh which is voltage * current * time.

I feel your confusion, and the best way to understand voltage, current and such is the parallel with the water. It behaves very similarly.

Think of a waterfall: - The height of the waterfall is the voltage. Higher is the height, more force the water will get. - The rate of flow of the water is the current. - The power is the rate of water * the height. - The energy is power * time.

Now you can think of a waterfall without any water going through, that is just basically a lake atop a mountain. This is potential energy.


To your question:

In this situation, if it takes V - 1 volts to move a charge from B -> C, but we are not moving any charge since there is no current, is the input 'B' still damaged? The Simple answer is Yes, because it is the "pressure" that will damage your component and as the metaphor above, you can burst a pipe by increasing the pressure without having the water (electron) to actually move.

You can also think of electron as balls inside a tube. enter image description here You can push the first ball harder and harder until the lead pops (your device breaks). Until the lead pops, the pressure would have increased but nothing actually moved.

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Understanding Voltage (Potential)

We know that a rock with mass m on top of a hill of height h has potential energy PE=mgh. The potential is just potential=gh and is the potential per unit mass. This is confusing because it is purposely vague. Instead, think of a dam holding back water. The potential energy of the water in the dam is something like PE=mgh where m is the mass of the water. However, we don't know how much water (mass) someone using the dam may need. They certainly don't need all of the water so using the total potential energy is useless. Some people need a little water and some need a lot. So the potential is much more useful and gives the user enough information to calculate the total mass or mass per second (current) required for their use case.

If I use the dam to turn my fan at a desired speed, then given the potential of the dam, I just need to calculate the volume of water required. If my neighbor wants a bigger fan, then given the potential of the dam, they need a larger mass of water and they can calculate that themselves independent of my fan.

Similarly, voltage is the potential per unit charge. A power supply has seemingly infinite charge that you can take advantage of depending on how much charge you need. Want to turn a fan? Just calculate the current (charge per second) required given the voltage potential. Neighbor wants to run a bigger fan? It will require a larger current.

So, I believe my analogy/explanation gives you the tools to understand why you can have voltage without current but cannot have current without voltage. In terms of dams and water, water will not flow (current) unless there is some potential; however, you can hold water at a potential (like behind a dam) without allowing water to flow. It is the same for electricity but instead of flowing water molecules and gravity, it is flowing electrons and the mutual repulsion of adjacent electrons.

Edit: This answer was completely revamped to address @ThePhoton's comment and I think better address the OP's question. My previous answer was technically wrong and although it helped me when I was learning circuits, it may just confuse someone else because it is incorrect.

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  • \$\begingroup\$ Voltage is potential, not potential energy. \$\endgroup\$ – The Photon Oct 18 '19 at 14:30

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