Solved Problems

Month: November 2010

  • Total Energy Stored – Circuit with Capacitors and Inductors

    Find the total energy stored in the circuit.

    find the energy stored in the circuit
    Fig. (1-28-1) – The circuit

    Solution
    The circuit contains only dc sources. Recall that an inductor is a short circuit to dc and a capacitor is an open circuit to dc. These can be easily verified from their current-voltage characteristics. For an inductor, we have v(t)=L \frac{d i(t)}{dt} . Since a dc current does not vary with time, \frac{d i(t)}{dt}=0 . Hence, the voltage across the inductor is zero for any dc current. This is to say that dc current passes through the inductor without any voltage drop, exactly similar to a short circuit. For a capacitor, the current-voltage terminal characteristics is i(t)=L \frac{d v(t)}{dt} . Voltage drop across passive elements due to dc currents does not vary with time. Therefore, \frac{d v(t)}{dt}=0 and consequently the current of the capacitor is zero. This is to say that dc current does not pass through the capacitor regardless of the voltage amount. This is similar to the behavior of an open circuit. Please note that unlike dc current, ac current passes through capacitors in general.
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  • Thévenin’s Theorem – Circuit with Two Independent Sources

    Thévenin’s Theorem – Circuit with Two Independent Sources

    Use Thévenin’s theorem to determine I_O.

    Thevenin's Theorem - Circuit containing two independent sources
    Fig. (1-27-1) – Circuit with two independent sources

    Solution
    Lets break the circuit at the 3\Omega load as shown in Fig. (1-27-2).
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