SOLUTION

Initial conditions

T=0- represents the instant before the event. In this case, the switch has been closed for some considerable time

T=0 is the Initial condition. The switch is closed i.e, switched on.

T=0+ is the instant after the event that means the switch has just opened.

Energy cannot change instantaneously for elements that store energy. Thus, there are no discontinuities allowed in current through an inductor or voltage across a capacitor at any time—specifically, the value of the variable remains the same at t=0⁻ and t = 0⁺.

At t=0⁻ a capacitor acts as an open circuit. Thus at a steady state at t=0⁻ we replaced capacitors by open circuits in the circuit.

At t = 0⁺  the capacitor voltage cannot change in going from t=0⁻ to t = 0⁺, we replace the capacitors with voltage sources whose values are the voltages at t=0⁻.

A capacitor maintains a constant voltage, and the process is often called smoothing the current. It accomplishes this by using its storage capacity—its capacitance—to either donate or accept electrons when there is a drop or a spike in voltage.

If there is a voltage drop in a circuit, the capacitor will push electrons toward the direction of the source voltage, acting as a voltage source. This may seem counterintuitive because we are used to thinking of electrons flowing in a single direction, from the positive to the negative terminals of a power supply. But electrons also flow “backward” in a circuit if the charge in the capacitor is positive compared to the voltage entering the capacitor. Electrons are still flowing positive to negative, but until the charges match, the capacitor acts as source voltage until it has exhausted its capacitance.