What happens in a capacitor's positive side

Discussion in 'General Electronics Chat' started by Yaşar Arabacı, Nov 14, 2014.

  1. Yaşar Arabacı

    Thread Starter Member

    Nov 11, 2014
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    I was reading http://www.allaboutcircuits.com/vol_1/chpt_13/1.html and I am having trouble understanding what happens in a capacitor's positive side.

    [​IMG]

    For example, in above schematics, I understand that some electrons move from battery to capacitor until there is enough voltage in between capacitor's each side. However, is there any current going on in the capacitor's positive side?

    [​IMG]

    Moreover, in this diagram, will there be any current on the positive side of the capacitor or is it just that electrons will go back on forth between capacitor and battery?

    In other words, is capacitor a dead end for electrons?
     
  2. #12

    Expert

    Nov 30, 2010
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    Remember, a capacitor is stupid. It only stands there while the battery arranges the electrons. In the first example, there will be a short time when electrons are moving on both sides of the capacitor, then they will stop. While moving, their magnitude of movement will be limited by the internal resistance of the battery and the resistance of the connecting wires. This is usually measured in microseconds.

    In the second example, this is a DC circuit. After the small amount of time required to reach steady flow, the capacitor is, as you said, a dead end.
    Only in an AC circuit will the capacitor experience being charged and discharged according to the frequency of the AC source.
     
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    It is if the voltage source is DC, and the capacitor has already charged so that it's terminal voltage is the same as the battery voltage, then the current flow goes to zero (no more net movement of electrons in the wires).

    Any real, practical capacitor will have some degree of DC leakage, so there will always be a tiny current even after the capacitor is fully charged.
     
  4. Yaşar Arabacı

    Thread Starter Member

    Nov 11, 2014
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    Hmm, I am having difficulty understanding point of capacitors if they basically stop the current after couple of microseconds.
     
  5. wayneh

    Expert

    Sep 9, 2010
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    There is an equal and opposite flow of electrons on opposite sides of the capacitor. If an electron enters one end, another leaves at the opposite end. The capacitor as a whole maintains a net zero charge, even as there is a separation of charge within the capacitor.
     
  6. Yaşar Arabacı

    Thread Starter Member

    Nov 11, 2014
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    Where does it go though? Into the battery?
     
  7. wayneh

    Expert

    Sep 9, 2010
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    Yup, exactly.
     
  8. Yaşar Arabacı

    Thread Starter Member

    Nov 11, 2014
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    Ok, so in this example;

    [​IMG]

    Assume that we adjusted potentiometer so that some electrons were pushed into battery, can you get those electrons back if you re-adjust potentiometer in a way that positive side of capacitor demands some electrons?
     
  9. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    If you move the pot wiper downward, the charge stored previously in the capacitor is being discharged, so current flows in the opposite direction.
     
  10. crutschow

    Expert

    Mar 14, 2008
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    Capacitors are used for many AC purposes, such a frequency filters, oscillators, power supply filtering, noise suppression, etc. If you study AC circuits you will understand.
     
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
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    One purpose on DC is for storage or ripple reduction on a rectified DC supply.
    If fed with AC the current continues to flow with each polarity reversal, with the voltage leading the current by 90° in a perfect capacitor.
    Max.
     
    Last edited: Nov 15, 2014
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