The charge flowing in a conductor changes with time as \( Q(t) = \alpha t - \beta t^{2} + \gamma t^{3} \). Where \( \alpha \), \( \beta \) and \( \gamma \) are constants. Minimum value of current is:
\( \alpha - \frac{\beta^{2}}{3\gamma} \)
\( \beta - \frac{\alpha^{2}}{3\gamma} \)
\( \alpha - \frac{\gamma^{2}}{3\beta} \)
\( \alpha - \frac{3\beta^{2}}{\gamma} \)