Ch$\mathrm{.}27$

$4.$ A $15\mathrm{.}0$ k$$ resistor and a capacitor are connected in series, and then a $12\mathrm{.}0$ V potential

difference is suddenly applied across them. The potential difference across the capacitor

rises to $5\mathrm{.}00$ V in $1\mathrm{.}30$ s$.($a$)$ Calculate the time constant of the circuit. $($b$)$ Find the

capacitance of the capacitor