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Charging of a capacitor

  1. Nov 6, 2009 #1
    1. The problem statement, all variables and given/known data

    We are examining an RC circuit with a scope. A square wave is applied to the circuit. Sketch the square wave and the trace giving the voltage across the capacitor. Explain your results.

    3. The attempt at a solution

    Untitled-6.jpg

    So I got something like this. Now the way understand it is that during the first half-cycle, the capacitor is being charged, so the electric potential across the capacitor increases to some value, then when the square wave switches, is it discharging or charging to a negative value?

    Just a little clarification there would be greatly appreciated!
     
  2. jcsd
  3. Nov 6, 2009 #2
    You essentially got the right idea. During each half-cycle, the capacitor discharges and then charges. Moreover, we can see from your second plot that as the capacitor is charging that the potential difference across it approaches some value asymptotically. Do know what this value corresponds to? Would this be the case if the period T of the EMF was reduced, say, by a factor of 10? Just something extra to think about.
     
  4. Nov 6, 2009 #3
    I would use the word "discharging" until the point in time when the capacitor voltage crosses the axis and is zero for an instant. After that I would say it is charging to the opposite polarity compared to the first half-cycle. I'm skeptical about the phrase "charging to a negative value." Regardless of the polarity, a capacitor always has zero net charge, but it has a charge separation between the two plates.
     
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