A dc voltage of $10\: V$ is applied across an $n$-type silicon bar having a rectangular cross-section and a length of $1\:cm$ as shown in figure. The donor doping concentration $N_{D}$ and the mobility of electrons $\mu_{n}$ are $10^{16} cm^{-3}$ and $1000\: cm^{2} V^{-1} s^{-1},$ respectively. The average time $(\text{in}\: \mu s)$ taken by the electrons to move from one end of the bar to other end is ________.