An RC circuit is connected across a DC voltage source through an open switch. Th

Question

An RC circuit is connected across a DC voltage source through an open switch. The switch is closed at t = 0 s. Which of the following is a correct statement regarding the circuit?

a) Once the capacitor is fully charged, there is no current in the circuit.
b) The capacitor charges to its maximum value in one time constant.
c) The current flows through the circuit even after the capacitor is fully charged.
d) The capacitor charges to its maximum value in two time constants.
e) The resistor and the capacitor share the applied voltage equally as a function of time.

Explanation / Answer

a-1) True, if RC-circuit is connecting in series. a-2) Fault, if RC-circuit is connecting in parallel (current is still flowing through resistor). b-1) True, if RC-circuit is connecting in parallel. (current is still flowing through resistor). b-2) Fault, if RC-circuit is connecting in series. c-1) Charging, will take 5 time constants (No exception: 63%, 86%, 95% 98%, 99%). c-2) discharging, will take 5 time constants (No exception: 37%, 14%, 5%, 2%, 1%). d-1) True, if RC-circuit is connecting in parallel. d-2) Fault if RC-circuit is connecting in series. Please keep this in mind: 1- Charging and discharging time will take 5 time constants = (5)X(RC). 2- At any charging time, capacitor voltage can be found by this equation Vc = [Vf] X [1-e^(-t/RC)]. 3- At any discharging time, capacitor voltage can be found by this equation Vc = [Vi] X [e^(-t/RC)]. Note: Vf = V final, Vi = Vinitial, e is the base of natural logarithms = 2.718.

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