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Homework Help: Series circuit problem - am I correct?

  1. Nov 18, 2008 #1
    1. The problem statement, all variables and given/known data
    A simple series circuit consists of a 150 ohm resistor, a 25 V battery, a switch and 2.5 pF parallel plate capacitor(uncharged initially) w/ plates 5mm apart. The switch is closed at t=0.

    What is the maximum electric flux and maximum displacement current through the capacitor?

    2. Relevant equations

    3. The attempt at a solution
    Maximum flux will be achieved when the capacitor is fully charged, at
    Vc = Vbat Vc = 25 V Q = (2.5*10^-12)(25) = 6.25 * 10 ^-11 C
    Electric flux = EA cos(theta)= qin/epsilon
    6.25*10e-11 / 8.85e-12 = <b> 7.06 Vm^2 </b>

    Displacement current = 8.85* 10e-12 * dFluxElectric/dt

    which = I/epsilon

    I need to find the Imax, so I used the formula for the charging of a capacitor:

    Q = Qmax(1-e^-t/RC)
    I = -dQ/dt = -Qmax/RC * (1-e^-t/RC) RC = 3.75 e-10

    the maximum I is Qmax/RC Qmax is calculated above to be 6.25e-11
    so Imax is .167 A

    so I think the maximum displacement current is .167 A

    Did I do this right?
  2. jcsd
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