Question

Let $q$ be the net amount (i.e. forward minus backward) of positive charge that flows in the forward direction across an area, in a given time interval $t$. Similarly, let $q_{-}$ be the net amount of negative charge flowing across the area in the forward direction. Then current $i$ equals

• A. $\frac{q_{+}+q_{-}}{t}$
• B. $\frac{q_{+}-q_{-}}{t}$
• C. $\frac{q_{-}-q_{+}}{t}$
• D. $\frac{q_{+}-q_{-}}{2 t}$

Answer 1

Answer: (B)

The flowing of negative charge in a direction is equivalent to flowing of positive charge in the opposite direction. Hence
$i=\frac{q_{+}-q_{-}}{t}$