- Joined Apr 1, 2016
I am studying for CET certification. I am hung up on a practice problem envolving capacitor discharge time. Here is the question. A 0.09 microfarad capacitor is charged to 220 Volts. How long in milliseconds will it discharged to a level of 110 V if the discharged resistor has a resistance of 20, 000 ohms? The answer is 1.25 milliseconds. I can up with 9 milliseconds. This is what I did. t=rc 20k times 0.09 micro farads then I multiplied by 5 time constants.