Question

If two parallel wires carry current in opposite direction
A. The wires attract each other.
B. The wires repel each other.
C. The wires experience neither attraction nor repulsion.
D. The forces of attraction or repulsion do not depend on current direction.

Answer 1

Hint Use right hand thumb rule to determine the direction of magnetic field formed by the first wire and force exerted by it on the second wire using the same rule. The same rules have to be used for the second wire and direction of force exerted on the first wire will be known.

Complete step-by-step solution :Consider two wires carrying current ${i_1}$ and ${i_2}$ in opposite directions

We will first use the right hand thumb for the first wire.
Align your thumb in the direction of current. The direction in which the fingers will curl will give us the direction of the magnetic field exerted by current ${i_1}$. Its direction will be into the plane towards the right of the first wire.
Now we will determine the direction of force exerted by this magnetic field on the second wire.
For this we will again use the right hand thumb rule. We will align our fingers in direction of current ${i_2}$ and then curl our fingers in the direction which our thumb points to give the direction of force.
We will find that our thumb points away from wire 1. That means the magnetic field repels the wire.
We will repeat the same steps for wire 2.
We will find that the wires repel each other.
So, option (b.) is correct.

Note:- To solve such questions quickly, one must be comfortable in using the right hand thumb rule and know what physical quantities fingers and thumb represent because we need to determine the direction of force applied by each wire on another.