Tag Archives: Energy

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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Problem 1-1: Power of Elements


Find the power of each element. Which one is supplying power and which one is absorbing it?

Power of Elements

Solution

a)  Passive sign convention,  P = V \times I = -8 W < 0 supplying power.
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