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# Capacitance, Voltage and Time Constant Question watch

1. 2.2x10^-3F Capacitor charged with a 12V battery. It is then discharged through a 10k(ohms) resistor.

So the voltage I'm given is 12V the time constant is 22s. I'm asked what will the voltage be across the capacitor after 22s? Does anyone know the answer?
2. Nevermind I found the answer. I used V = V(0)e^-(t/RC) equation to get 4.41V.
3. (Original post by NatKH)
Nevermind I found the answer. I used V = V(0)e^-(t/RC) equation to get 4.41V.
FWLIW The rule of thumb is that it decays by 63 (ish) % after one time constant... or decays to 37 (ish) % of it's original value.

Of course the equation will give you an answer even when the time elapsed isn't a whole number of time constants.

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Updated: October 21, 2017
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