Charging and discharging a capacitor CRO....:/

Discussion in 'Homework Help' started by Electronicsrookie, Feb 22, 2011.

  1. Electronicsrookie

    Thread Starter New Member

    Nov 28, 2010
    Hi guys, I'm in a big prob. So I had practical on charging and dis. a capacitor(100microfarad, electrolytic).

    Dc supply was set to 15v.
    Capacitor was in series with a 33k resistor.
    CRO CH1 was parallel with capacitor(to measure Vc).

    So here's the bug.
    Charge the capacitor. Done
    Q: Pull out capa and turn off power. Insert the 33k resistor and note the observation on the CRO.
    A: I dono how to describe this....:/
    q:Discuss what is observed on CRO during charging and discharging.
    Notes plz.
  2. narasimhan


    Dec 3, 2009
    Just switch off the supply(some supplies open when switched off. So better reduce the voltage to zero) and see how the Vc slowly decreases to zero that's discharging.

    Thats pretty lame. If you pull out the cap chances are that you finger will touch the two pins of the caps and hence they discharge. Moreover caps used in labs leak pretty fast so I seldom think you'll be able to view the discharge behaviour
  3. Georacer


    Nov 25, 2009
    What's a CRO? I take it you want to observe the voltage dropping gradually with some equipment.

    Turning the supply voltage to 0 will not do for you, because the power supply will actively discharge the capacitor. Switching it off may do the same thing, but I 'm not sure about that.

    The correct methodology is to put the capacitor in a breadboard, and connect it to the power supply, not directly on its pins, but rather through a neighbouring pin / jumper wire.

    Then connect your measuring equipment and afterwards connect the resistance. I think that the voltage will remain for long enough to observe the phenomenon.
  4. Adjuster

    Well-Known Member

    Dec 26, 2010
    He means an oscilloscope - old fashioned terminology: Cathode Ray Oscilloscope. Of course, most 'scopes these days don't use a CRT!
  5. Georacer


    Nov 25, 2009
    Oh, I see. Thanks for the clarification, Adjuster.