Equivalent resistance for resistors in series:

$\overline{){{\mathbf{R}}}_{{\mathbf{eq}}}{\mathbf{=}}{{\mathbf{R}}}_{{\mathbf{1}}}{\mathbf{+}}{{\mathbf{R}}}_{{\mathbf{2}}}{\mathbf{+}}{\mathbf{.}}{\mathbf{.}}{\mathbf{.}}{\mathbf{+}}{{\mathbf{R}}}_{{\mathbf{n}}}}$

For an LR circuit, the variation of current as a function of time is:

$\overline{){\mathbf{I}}{\mathbf{\left(}}{\mathbf{t}}{\mathbf{\right)}}{\mathbf{=}}{{\mathbf{I}}}_{{\mathbf{0}}}{{\mathbf{e}}}^{\raisebox{1ex}{$\mathbf{-}\mathbf{t}$}\!\left/ \!\raisebox{-1ex}{$\mathbf{z}$}\right.}}$

Equivalent resistance in the circuit:

R_{eq} = 200 + 100 = 300Ω

At t = 0 s, the current in the circuit in the figure is I_{0}. At what time is the current ½ I_{0}? Express your answer with the appropriate units.

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