Question

Two boys $A$ and $B$ are sitting at two points in a field. Both boys are sitting near assemblage of charged balls each carrying charge $+3 e$. $A$ throws $100$ balls per second towards $B$ while $B$ throws 50 balls per second towards $A$. Simultaneously, find the current at the mid-point of $A$ and $B$.

• A. $i=3.4 \times 10^{-17}$ A from $A$ to $B$
• B. $i=2.4 \times 10^{-17}$ A from $A$ to $B$
• C. $i=3.4 \times 10^{-17}$ A from $B$ to $A$
• D. None of the above

Answer 1

Answer: (B)

Let mid-point be $C$ as shown
Current from $A$ to $B, i_{1}=100 \times 3 e=300 e \quad\left(i=\frac{\Delta Q}{\Delta t}\right)$
Current from $B$ to $A, i_{2}=50 \times 3 e=150 e$
Net current, $i=300 e-150 e=150 e$ towards right $i=150 \times 1.6 \times 10^{-19}=2.4 \times 10^{-17} A$ from $A$ to $B$