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Help with understanding capacitance

  1. Dec 19, 2009 #1
    my book does not fare well in explanations, thus I have a few questions

    if the capacitor plates hold energy, how does this energy become released in certain applications? what are some common applications of capacitors?

    if the voltage difference in parallel capacitors are the same, why is the voltage difference in series capacitors different? why do they add up to be the overall voltage of the battery?

    more questions as I read more about this

    sorry if they're stupid questions, book sucks kinda.
  2. jcsd
  3. Dec 19, 2009 #2


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    Hi johnnyies! :smile:
    It's released (not all at once, but exponentially) when the circuit (joining the two plates "the long way round") is completed.
    It has to be, or charge would flow between the two capacitors.
    For the same reason as for resistances. :smile:

    (There's nothing "magic" about capacitors … just think about what the charge does … the total charge is conserved, and it moves if there's a voltage difference :wink:)​
  4. Dec 19, 2009 #3
    yes, but how do we release that charge from the capacitors?
  5. Dec 19, 2009 #4
    In a DC circuit the charge stored can only be released if you give the capacitor a path to release it through. For instance you could charge a capacitor using a DC power supply and then disconnect the capacitor and use it as a temporary power source in another circuit.

    You might be struggling to understand them because you're focusing on its DC applications, in DC circuits with ideal conditions capacitors have little use. However, capacitors are extremely useful in AC circuits due to the impedance being affected by frequency (in proportion to its capacitance).

    In AC circuits its useful to think of capacitors in terms of impedance. Its impedance is higher with lower frequencies (with a frequency of 0 it's open circuit) and its impedance is lower when the frequency is higher (at infinite frequency it's short circuit).
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