Question

Two free parallel wires carrying currents in the opposite directions

• A. attract each other
• B. repel each other
• C. do not affect each other
• D. get rotated to be perpendicular to each other

Answer 1

The correct option is B repel each other

Let wire on RHS carry current vertically upwards and wire on LHS carries current vertically downwards then the direction of magnetic field at a postion where RHS wire is there due to LHS wire is out of the plane. Now RHS wire is a current carrying conductor placed in a magnetic field due to LHS wire. Similarly LHS wire is a current carrying conductor placed in a magnetic field due to RHS wire. Therefore, they both will experience force.
Now in RHS wire current is vertically upwards and direction of magnetic field is out of the plane. Since direction of force is given by $F=\overrightarrow{dl}\times \overrightarrow{B}$ therefore, force acting on RHS wire is towards right and by applying similar method we find that force acting on LHS wire is towards left. Therefore, they both repel each other.