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Can someone please help me understand voltage

  1. Dec 17, 2013 #1
    For some reason, i feel like the concept of voltage is escaping my grasp. I've done much research on these forums and through texts, and come across answers that seem quite well thought out, but still cant grasp the fundamental concept of what voltage is.

    I could explain (regurgitate) the definition of voltage in many ways, and plug it into equations, but when it comes to testing my fundamental understanding of it as a natural concept, I fall short.

    Ill explain what i know, and what i don't, and i have some theoretical questions which i hope will help give me a better understanding.

    Here is what i know (I think)
    1. Voltage is electrical potential energy. It represents an imbalance of charge distribution.

    2. This means that given a sufficient conductor, the electrons will do work by moving to a state of equilibrium to correct this imbalance.

    3. Voltage must be measured between two points, because it can only exist in relation to an imbalance between one point and another.

    4. Measures of voltage determine the work which can be done as a result of the imbalance?

    5. The quantity of voltage in a battery would not change if you increased the size of the battery. It would only change if you increased the average negativity charge density in the negative terminal?


    Here is what i dont know or have questions about:
    1. So, increasing voltage increases current because higher voltage means a higher disequilibrium from the source, meaning more "pressure" on the electrons to move? Given a fixed wire diameter, does that means higher voltage would make electrons move faster?

    2. Why do resistances in series add together? I dont understand. I picture a resistor as a bottleneck, in that the entire circuit is limited by the resistance of the most resistant component. But this is clearly wrong. Is it more correct to imagine that every time electrons travel through a resistor, they have to do more work and lose some of their ability to do future work, and have lower and lower energy the more resistors they go through?

    3. If a current/stream of electrons begins to flow and is travelling through a wire with 1 ohm resistance, and goes through a 5 ohm resistor, then back to a 1 ohm resistance wire, since resistance decreases, would it speed up again upon exiting the 5 ohm resistor? If so, I'm assuming its new speed (relative to its initial speed upon entering the circuit) would be proportional to the fraction of remaining voltage after the total voltage drop up to that point?

    4. When a battery dies, i'm assuming that its voltage isnt at 0. Does a dead battery just no longer have the minimum voltage required to supply the circuit with enough power to power the device? In that case does that mean that dead batteries could still power a circuit with less resistance or lower power demands?

    5. This quote from wikipedia confuses me: "In a series circuit, the current through each of the components is the same, and the voltage across the circuit is the sum of the voltages across each component". What does it mean that components "have voltage". Im assuming this means the drop in voltage from before the component compared to after, right? But what is the reasoning for saying the component "has" voltage? Is it trying to express the quantity of work done (i.e. heat emitted) from that component?

    6. Last one, another wiki entry: "In a parallel circuit, the voltage across each of the components is the same". This confused me, but i think i just figured it out. If a current is flowing through multiple paths, it would take the path of least resistance to its destination, thus if a parallel circuit has a 1 ohm resistor and a 5 ohm resistor in parallel, both would have the same voltage drop, but the current flowing through the 5 ohm resistor would be 1/5th the value of the 1 ohm?


    Thanks for taking the time to read my post. I hope i didnt get everything terribly wrong XD

    Looking forward to whatever answers you guys can offer!
     
    Last edited: Dec 17, 2013
  2. jcsd
  3. Dec 17, 2013 #2

    HallsofIvy

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    Staff Emeritus
    Science Advisor

    Yes, that's correct- voltage is energy. You might think of it as the height of a hill that water is pouring down.

    Yes, if there is a channel for the water to flow down, then it will.

    Absolutely, just as the potential energy difference between two points is "mgh" where h is the difference in heights.

    Yes, voltage is energy and work is a form of energy.

    Right. The height of a hill does not depend upon the size of the reservoir at the top of the hill.

    Yes, just as a higher reservoir of water will give more energy to the water flowing out of it and, given the same size channel, move faster.

    Yes, continuing to use my water analogy, as the water passes through narrow channels, the friction on the sides and bottom reduce its energy and slow it down. Of course, passing through a channel with resistance "A" and a channel with resistance "B" is the same as passing through a channel with resistance "A+ B".

    No, it has lost energy passing through the 5 ohm resistor and will then lose more energy passing through the 1 ohm resistor. It simply loses less energy than before, it doesn't regain energy.

    No, voltage does not reduce- it is the amount of electricity, the current, that runs out.

    That really should be "voltage drop" across each component. Just as, in order for water to run through a narrow channel, there must be a drop in height between the start and end of the channel, so for current to run through a resistor, there must be some drop in potential energy or voltage.

    Yes. Again, if water has two channels to pass through, one narrower than the other, the water will move faster through the narrower channel. The total energy flow through them will be the same.


     
  4. Dec 17, 2013 #3

    rcgldr

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    Homework Helper

    Voltage is a potential, it's the potential energy per unit charge, assuming a postive unit of charge.

    The height analogy in the previous post is similar. For an object at small distance from the earth's surface, the gravitational potential is "g h" (g = gravitational acceleration, h = height above earth's surface).
     
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