A coil of self inductance 10 mH and resistance 0.1 Ω is connected through a switch to a battery of internal resistance 0.9 Ω. After the switch is…

A coil of self inductance $\displaystyle 10$ mH and resistance $\displaystyle 0.1 \Omega$ is connected through a switch to a battery of internal resistance $\displaystyle 0.9 \Omega$. After the switch is closed, the time taken for the current to attain $\displaystyle 80$% of the saturation value is : [take $\displaystyle \ln 5=1.6$ ]