1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Electric Potential Energy in Different parts of Circuit

  1. Apr 7, 2014 #1
    When a positive charge leaves the positive part if the battery it has maximum electric potential energy then as it moves through a wire with a zero resistance the charge is closer to the negative side of the battery.

    So, while travelling in a wire in a circuit does it lose electric potential before it reaches a resistor even without resistance?
  2. jcsd
  3. Apr 7, 2014 #2
    IF there really is no resistance, there will be 0 field in the wire, and the charge won't lose any potential energy.

    - A positive charge will only lose energy when moving in the direction of the electric field.

    - The source of the field in the wire is not only the battery, but also charges in the wire itself.

    - in an ideal conductor, the charges will rearrange themselves, so there is no field in the conductor.
  4. Apr 7, 2014 #3


    User Avatar
    Science Advisor
    Gold Member

    Every piece of wire has some resistance - you can find tables of resistivity (resistance per unit of length):

    If you have a long enough piece of copper wire you can measure the total resistance with an ordinary ohm meter.
  5. Apr 7, 2014 #4


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    If the connecting wires have no resistance then no energy is needed to get the charges through and no Potential is lost.
    If you connect such a wire (a great thick piece of copper, for instance) to a battery then the only resistance in the circuit will be in the battery itself (its internal resistance) All the PD will be developed inside the battery and a lot of current will flow, over-heating, blowing up or, at least draining the battery very fast because all the power is dissipated inside the battery.

    I do really not know what you mean by this.
  6. Apr 7, 2014 #5

    Then what will make the current move since there's not an electric field ???
  7. Apr 7, 2014 #6
    What field do you need to move electrons through a zero resistance conductor? :smile:
  8. Apr 7, 2014 #7


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    You are suffering here from the consequences of getting involved with Zeros or Infinities and trying to apply them to a physical situation.
    If the wire has zero resistance then that implies (amongst other things) an infinite amount of charge is available. That means you can put as much in one end and get the same amount out of the other end without any work being done or energy being dissipated. Even if you tried to involve the Kinetic Energy of these charges (as in many bad models of electricity), the speed would be zero - so even that doesn't give you any energy to worry about.
    In a situation like this, it would be better to consider a very low resistance and, hence, a very low / negligible PD - which is what all connecting lines (wires) are assumed to be like on a schematic diagram. So there is negligible Power lost in the wire.
  9. Apr 7, 2014 #8
    theoretically, how can an object have zero resistance ?
  10. Apr 7, 2014 #9
    If there is no scattering event suffered by charge carriers, then the resistance is theoretically zero.
    In superconductors this is also practically so.

    A perfect lattice does not scatter electrons. Just modulates their wave-function, effect described by the "effective mass". The motion of electrons through a lattice is a quantum process. Classical analogies are just approximations.
  11. Apr 7, 2014 #10

    I don't get it, are the electrons scattered by a contact or a non-contact force ??
  12. Apr 7, 2014 #11
    What would you mean by "contact" force at microscopic level?
    The force is not such an useful concept in quantum mechanics.

    The main scattering processes are due to vibrations of the lattice, impurities and lattice defects.
    This is in single crystals. In poly-crystalline metals the grain boundaries will have an effect.
  13. Apr 7, 2014 #12
    Why Does it have to vibrate to cause scattering,
  14. Apr 7, 2014 #13
    I think the question is "why doesn't" if it's a perfect, periodic lattice, right?
    This is pretty much what Felich Bloch "discovered" by applying quantum mechanics to the motion of an electron in a periodic lattice, in 1930s. The fact that this was an important result shows that there was no classical explanation for it and no way to "expalin" it in terms of classical particles.
    It has to do with the "wave nature" of the electron.
  15. Apr 7, 2014 #14

    I still don't get it, if I brought up the gravitational analogy
    I would say that even if the earth's atmosphere is vanished, at it became vacuum, object that are lifted above the earth surface will fall back down losing their P.E, then energy is lost
    Naturally responding to the nature direction of the graviton am field whether there's a resistance or not, and if there isn't any gravitational field then there is no such thing as potential energy and it will never fall back again.
  16. Apr 7, 2014 #15
    the charges still loose their energy in the end.positive charges reach negative ones and unite and the potential difference is ultimately lost.the only difference that in a superconductor they did not loose any of that potential difference while traveling
  17. Apr 7, 2014 #16


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    Firstly, the 'gravity'/ planetary model is not very good for describing the atom. Also, introducing gravitons really cannot help at this stage in your knowledge. "Graviton" constitutes little more than a buzzword in the context of what we are discussing. It would help to approach this subject from the conventional standpoint until you know a lot more. (20 million flies cannot be wrong).
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook