A resistance $R$ and a capacitance $C$ are connected in series to a battery of negligible internal…
A resistance $R$ and a capacitance $C$ are connected in series to a battery of negligible internal resistance through a key. The key is closed at $t=$ 0 . If after $t$ sec the voltage across the capacitance was seven times the voltage across $\mathrm{R}$, the value of $\mathrm{t}$ is