Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

What is the role of displacement currents in a circuit?

  1. Dec 2, 2016 #1
    Please help me with this. I am having a hard time understanding the role of displacement currents in a circus. The common knowledge is actual current is the movement of electron in a circus. Now, if there is a gap and an AC source, there would be an electric displacement field and a displacement current in that gap. But that displacement current is not the movement of electrons. Then what happen with the electrons once they reach one end of the gap? Where do they go? And what happen to the ground electrode of that circus if there is no electron to ground?
    I am sorry if this question seams silly to you, but this is not my strong point so please be patient and help me. Thank you!
  2. jcsd
  3. Dec 2, 2016 #2


    User Avatar
    Homework Helper
    Gold Member

    I guess you mean circuit and not circus hehe.

    The electrons when they reach one end of the gap they stay there and accumulate. The two edges of gap can be modeled as some sort of capacitor with very small capacitance C, and because the capacitance is small, even in an AC driven circuit the current I (both the displacement current and the electron current) will be very small when we have a gap. However if the frequency ##\omega## of the AC becomes very large, then because ##\omega C## will not be so small and so the current will not be so small either.

    I am not sure I understand your second question, but if you mean that the ground electrode is not connected to some big and good electricity conductor then all that it happens is that the potential at the ground electrode will not actually be 0, as we want it to be.
    Last edited: Dec 2, 2016
  4. Dec 2, 2016 #3
    Hello Delta, thank you for your answer. And sorry about my English keke.

    So if the two edges work like a capacitor then with an AC source, it would be like the continuously charging and discharging cycles of the capacitor. I can imagine that without a grounding conductor. But then if the system is ground, I mean the role of grounding is to lead exceed electrons through a conductor to the ground right. Then if there is a lost of electron on one side, how can the process of recharge continue?
    Please see the picture to understand what I mean.

    Attached Files:

  5. Dec 2, 2016 #4


    User Avatar
    Homework Helper
    Gold Member

    You basically mean that there is a leakage current to/from the ground (electrons that come from or go to the ground). Yes this is true, but for small frequencies and with the simplifying assumptions made in circuit theory it is neglected. Only if you want to do complete field analysis of the circuit, you take into account such currents.
  6. Dec 4, 2016 #5
    Thank you Delta!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted