Finding capacitance in a RC circuit?

Question

Question: If the half-life for an RC circuit is 8.7 ms and the resistor is 100 ohms, what is the capacitance?

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I have no idea where to start on this one, if you know how to solve it any tips would be greatly appreciated!

Answer 1

We need the natural period of the circuilt, which is the half life divided by the natural log of 2.  This gives us 8.7/0.6931 = 12.55 milliseconds.  This is the product of resistance and capacitance, which makes the capacitance 125.5 microfarads.