A capacitor with an initial potential difference of$100$Vis discharged through a resistor when a switch between them is closed att$=0.$ Att$=10\mathrm{.}0$s$,$ the potential difference across the capacitor is$1\mathrm{.}00$V$.($a$)$ What is the time constant of the circuit? $($b$)$ What is the potential difference across the capacitor att$=17\mathrm{.}0$s$?$