Help Voltage drop is driving me insane

  1. Help!!!!! Voltage drop is driving me insane!!!!

    1. If the Voltage Drop across a load increases due to its added resistance, what happens to the voltage drop across other segments on the circuit?

    2 Why does resistance decrease Voltage (create voltage drop) if the Voltage is a Force "APPLIED" to the entire circuit.
     
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  3. Defennder

    Defennder 2,616
    Homework Helper

    Re: Help!!!!! Voltage drop is driving me insane!!!!

    1. The voltage drop across a closed loop in a circuit is equivalent to the emf driving the current around that loop. The emf is constant throughout the loop regardless of resistance. So that means all the voltage drops would sum up to the same emf. What happens if a particular voltage drop across a load increases? What does that say about the sum of the voltage drop around the same loop across other circuit elements?

    2. Voltage isn't exactly a "force". It's the amount of energy provided to a unit of charge when it travels in a closed loop in the circuit. So the proper question would be why does the energy of electrons or charge carriers diminishes when it goes through a circuit element?
     
  4. Re: Help!!!!! Voltage drop is driving me insane!!!!

    I thought that voltage was the amount of FORCE that was inherent because of.....to equalize a "surplus" of electrons, relative to a deficiency of electrons...then RESULTING proportionally in the amount of "energy" expended/provided to a unit of charge because of that force...


    Yes, I guess this is the real question
    you are basically saying the force is applied the same everywhere but the energy is not, can you elaborate....i need detail.
     
  5. Re: Help!!!!! Voltage drop is driving me insane!!!!

    think of the electrons as water. voltage would then be pressure.
     
  6. Re: Help!!!!! Voltage drop is driving me insane!!!!

    Well, the energy contained in a circuit may be given by W=qV.

    When you differentiate this equation with respect to time, you get

    [tex]P=\frac{dW}{dt}=\frac{dq}{dt}V=IV[/tex]

    So, for a given applied voltage, the energy must be constant (law of conservation of energy), and since V cannot be changed, the current varies across the load.

    Since the net load may be a variable, the energy available to the load is still constant, but the amount of charge moving through the various parts of the load will vary.
     
  7. Defennder

    Defennder 2,616
    Homework Helper

    Re: Help!!!!! Voltage drop is driving me insane!!!!

    I never tried thinking about it in terms of force because it's quite confusing and you'll end up confusing the notion of "force" in mechanics and circuits. Note that there isn't a surplus or deficiency of electrons anywhere in a circuit, unless there's capacitors involved.

    As above, don't think of it as "force". The energy provided to a charge to move through all the circuit elements in a closed loop is the emf. The resistance of a circuit element 'saps' the energy provided to the electron (though this doesn't mean the speed of the electron is reduced!), until it reaches the negative terminal of the battery and "gets recharged" again.
     
  8. Re: Help!!!!! Voltage drop is driving me insane!!!!

    I don't get it.....you say don't think about it in terms of force....but, yet you say EMF
     
  9. Re: Help!!!!! Voltage drop is driving me insane!!!!

    i was refering to the surplus or deficiency of electrons manipulated at the source, like in a battery.
     
  10. Defennder

    Defennder 2,616
    Homework Helper

    Re: Help!!!!! Voltage drop is driving me insane!!!!

    You shouldn't take terms too literally. The electromotive force is not a "force" in a literal sense any more than imaginary numbers are purely imaginary. There are a lot of physics terms which are coined from the original groundbreaking papers whose authors were wedded to an antiquated worldview and philosophy.

    See:
    http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elevol.html#c2

    And there isn't any surplus or deficiency of electrons in a cell. The electrons move from the positive to the negative terminal in the circuit because of the electric field associated with the potential difference provided by the cell. The electrochemical potentials cause the electrons to move from one half-cell to the other:
    http://en.wikipedia.org/wiki/Electrochemical_cell
     
  11. Re: Help!!!!! Voltage drop is driving me insane!!!!

    ok now i am VERY confused....how is there a potential difference if there is no surplus or deficiency of electrons???
    as far as i know a deficiency or surplus of electrons will make an atom more positively or negatively charged...doesn't the chemical reaction in a cell generate the separation of charge???

    on wikipedia is say The source of a true electric field is the electric charge that has been separated by the mechanism generating the emf.
     
  12. Re: Help!!!!! Voltage drop is driving me insane!!!!

    obviously
     
  13. Defennder

    Defennder 2,616
    Homework Helper

    Re: Help!!!!! Voltage drop is driving me insane!!!!

    Hi, perhaps this page would help:
    http://hyperphysics.phy-astr.gsu.edu/hbase/electric/battery.html#c2

    Basically what it says is that there is a pair of oxidation/reduction reactions which occur simultaneously. The electrons given up by oxidation is then provided as a reactant for the reduction which occurs at the cathode. The electrons given up by oxidation then travel around the ciruit to reach the cathode and that is the source of current. I don't know what Wikipedia means by a "true electric field".

    This is in reference to what?
     
  14. Re: Help!!!!! Voltage drop is driving me insane!!!!

    Oh yes, this question has been driving me insane for a while now.

    Voltage is the integral of the electric field over distance between the two sources of the electric field.

    http://img525.imageshack.us/img525/7549/circuit56wc7.jpg

    So as far as direct current from a battery is concerned, Each terminal of the battery has so many electrons missing on the positive side, and the same amount of electrons added to the negative side. Each terminal has the same exact electric field but with opposite charge.

    In the case of a battery, distance is insignificant. So the voltage of the battery is determined mostly by the strength of the electric field coming from the 2 terminals.

    Now keeping this in mind, lets think about voltage drops due to resistance.

    I often think of this analogy. Voltage is like the potential energy that a ball feels on top of a roof. The potential energy is determined by gravity and the height of the ball. Nothing else.

    Electric field is exactly like gravity. Heck look at coulombs law and Newton’s law of gravitation. They look almost identical.

    So the voltage is determined only by the strength of the electric field and the distance between the positive and negative terminals. By connecting a really long circuit you add to that distance, but regular circuits are very short. So distance doesn’t really matter.

    Okay now going back to the analogy. I always thought of resistance the same as friction or air resistance. So now think of the ball falling off the roof. It has some velocity V.

    Air resistance affects its velocity.

    Now here is the main point!!!!! Air resistance doesn’t effect the potential energy of the ball. The only thing which affects that is gravity (which never changes ) and distance.

    So if current is the same as velocity, and resistance in a circuit the same as air resistance, the voltage should NOT be affected by resistance. It should only be affected by distance which is too tiny to matter.

    But why is it affected? This question has driven me insane for a year now.

    I have an idea though. Resistance in a circuit is not like air resistance. Instead resistance in a circuit blocks out the electric field between the electron traveling through the circuit and the positive electrode. So then Voltage is decreased, which in turn decreases current by ohm's law.

    That is the only way it makes sense to me!!! Please explain if I'm wrong.
     
  15. Re: Help!!!!! Voltage drop is driving me insane!!!!

    voltage could be thought of as height above ground. but instead of just falling straight to the ground imagine a slide twisting and turning around from the top to the bottom. the energy released is not effected by the route the slide takes.

    but I really think water pressure makes a better analogy. the mass of the water represents inductance. a diaphragm in the pipe represents capacitance. friction as resistance.
     
  16. Re: Help!!!!! Voltage drop is driving me insane!!!!

    Well yes exactly. The Potential energy is NOT affected. Then why is Voltage affected? Voltage is potential energy.

    What is affected is kinetic energy of the ball or electron or whatever you want. That is why current goes down due to resistance. Current is kinetic energy dependant, while voltage is potential energy dependant.

    Btw I'm just a mere university student with electrical engineering as a major who loves science. I'm just throwing my ideas out according to my understanding. I want you older and more experienced professors or whoever you are at this site lol, to explain the world to me and the rest of us mere students. :wink:
     
  17. Re: Help!!!!! Voltage drop is driving me insane!!!!

    I an not o professor. I probably know less about it than you do.

    what do you mean 'why is the voltage affected'? how do you think its affected?
     
  18. Re: Help!!!!! Voltage drop is driving me insane!!!!

    Well I mean the title of this thread. Voltage drops. When solving a circuit the voltage inside of the resistor drops. Why?
     
  19. Re: Help!!!!! Voltage drop is driving me insane!!!!

    if you have water at one pressure connected by a hose to another container at a lower pressure water will flow from one to the other. water will continue to accelerate through the hose until the pressure drop from friction equals the difference in pressure.
     
  20. Re: Help!!!!! Voltage drop is driving me insane!!!!

    Yea I guess that makes sense. Thanks. I'm not really used to thinking of water pressure, I'm more used to thinking of it the way I described earlier.

    I think when it comes to electrical engineering, its easier to not question why voltage drops, but to just accept that it does and to solve for it correctly. :wink:
     
  21. Re: Help!!!!! Voltage drop is driving me insane!!!!

    As far as anaogies go, I don't want to know what "It" is like.
    I want to know what "It" is......And I also want to know anything about "It's" WHYs..and HOWs

    I know that voltage is a measurment that is valid when refering to OPEN terminals, and not in effect when part of a closed circuit........In an OPEN supply measurement there is no generated EMF other than that of the supply.

    I also know that when you measure the voltage across a device with a closed circuit you are NOT reading the supply voltage anymore, but instead VOLTAGE DROP, in relation to the given current and known resistance of your meter..... you are measuring the suppy EMF acting on the rest of the circuit, or the "generated" EMF, known as Voltage drop.

    again....spare me the lame analogies,

    Why does the energy of electrons or charge carriers diminishes when it goes through a circuit element?

    please refrain from explaining things just simply because of OHMs law....OHMs law is described or "DEFIJNED" BY what happens....it does NOT DEFINE WHAT IS HAPPENING.
     
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