(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A 1.47 micro F capacitor is charged through a 123 Ohm resistor and then discharged through the same resistor by short-circuiting the battery.

While the capacitor is being charged, find the time for the charge on its plates to reach 1/e of its maximum value.

2. Relevant equations

q = Q_final[1-e^(-t/RC)], (q)/(Q_final) = [1-e^(-t/RC)]

3. The attempt at a solution

Firstly, forgive my ignorance.

Well, I know that when charging an RC-circuit, the current decreases exponentially with time and the charge on the capacitor increases with time as the capacitor charges. Using the above equation, I assume we should be able to calculate a time constant, when t = RC, so that the charge would be 1-1/e of its final value. Though this will probably be straightforward to everyone else here, it's still not clear for me how to approach this. If I straightforwardly find the product of the capacitance and resistance, I'm only finding the aforementioned 1-1/e of the maximum value, correct? I'm beginning to become very muddled about this problem, and I can't tell if I'm fudging the the math (perhaps I just need an Algebra problem-solving review), or if my conception of the problem is way off. If anyone can provide a suggestions or hints as of how to approach this problem, I would greatly appreciate it. I apologize if this has been a waste of your time.

Thanks,

Austin

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# Homework Help: Charging an RC Circuit

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