$A$ long wire $A$ carries a current of $10 \, A$. Another long wire $B$,which is parallel to $A$ and separated by $0.1 \, m$ from $A$,carries a current of $5 \, A$ in the opposite direction to that in $A$. What is the magnitude and nature of the force experienced per unit length of $B$ $(\mu_0 = 4\pi \times 10^{-7} \, T \cdot m/A)$?

• A
  Repulsive force of $10^{-4} \, N/m$
• B
  Attractive force of $10^{-4} \, N/m$
• C
  Repulsive force of $2\pi \times 10^{-5} \, N/m$
• D
  Attractive force of $2\pi \times 10^{-5} \, N/m$