Problem: An RC circuit has a time constant of 68 micro-seconds. The capacitor is charged to 14 V. How much is the voltage across a resistor after 136 micro-seconds of discharge?
Attempt: What I know is that the time the capacitor fully discharge is at 5 Time constant. Then the formulas involved are: Time Constant = R*C and Voltage at the capacitor (Vc) = Vm (e^-t/time constant) but no resistor value were given so:
Time Constant = R*C ; R = (68 x 10^-6) / 14 = 4.86 micro-Ohms. I assumed that Vc = Vm at this time constant. And now I don't know what to do next. I think we have to get the Vc after 136 micro seconds then subtract it from the total voltage.
Question: How to answer this kind of problems? By the way, the correct answer is 1.96 V from the key to correction. Any help would be appreciated.