Answer
$1.099 \tau$
Work Step by Step
The formula for capacitor discharge is $Q = q_0 * e^\frac{-x}{\tau}$. To find the point at which the capacitor has lost the first third of charge, we set $e^{\frac{-x}{\tau}}= \frac{1}{3}$.This occurs when $\frac{x}{\tau} = \ln 3 = 1.099$. Therefore the answer is $1.099 \tau$.
