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Time required to charge a capacitor

by Liketothink
Tags: capacitor, charge, required, time
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Liketothink
#1
Oct7-09, 09:22 PM
P: 69
1. The problem statement, all variables and given/known data
A capacitor with a capacitance of C = 28.7 μF is slowly charged by a constant current of I = 63.2 nA. How long does it take to charge the capacitor to a voltage of V = 28.9 V?


2. Relevant equations
q=cvb(1-e^(-t/RC))
Vb=IR+QC


3. The attempt at a solution
I have tried to solve for R by R=I/V but I don't know how to solve for t because Q is not given, and I don't know how to find it. Any ideas? I only got a couple hours left. Any help is greatly appreciated.
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kuruman
#2
Oct7-09, 09:38 PM
HW Helper
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P: 3,442
The statement that the current is constant says that you are in the linear region all the way to charging the capacitor to 28.9 V. You can calculate how much charge is on the plates when the voltage is 28.9 V and from this the time it takes for this charge to accumulate at a constant rate. The exponential is not needed here.


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