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... asked in Science & MathematicsPhysics · 1 decade ago

Capacitors and resistor question?

When the 1000 microF capacitor is fully charged, it is removed from the circuit and connected across a 10 ohm resistor. What is the total energy dissipated in the resistor? (V=9V).

Not sure if I just use E=1/2 CV^2.

Thanks

1 Answer

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  • Mohasa
    Lv 4
    1 decade ago
    Favorite Answer

    Short answer: yes, E = 1/2 CV^2 is the total energy dissipated in the resistor.

    Basically, you're discharging the capacitor via a resistor. With time, all the energy

    stored in the capacitor in the electric field is dissipated via the resistor. The equation

    you gave is the total energy stored in the capacitor.

    -----------------------------------------------------------------

    If you're up to the task, you can prove it!

    From P = IV, and E = Pt

    or dE = Pdt = IVdt = V²/R dt

    This integration is done from t=0 to t = infinity.

    Use V = Vp*exp(-t/RC) and

    E = ∫{Vp*exp(-t/RC)}²/R dt

    to establish that

    E = Vp²C/2, Vp is the peak (fully charged) voltage across the

    capacitor (resistor as well).

    ---------------------------------------------------------------------------

    Hope this helps

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