Current is passed through two parallel conductors in the same direction. If the conductors are placed near each other, they will------------------

Analyze the question: Two parallel wires carry current in the same direction. What force acts between them?

Concept: A current-carrying conductor produces a magnetic field around itself. When a second current-carrying conductor sits in that field, it experiences a force (F = BIL). This is the basis of the definition of the ampere.

Rule for parallel conductors:

• Currents in the same direction → the wires attract
• Currents in opposite directions → the wires repel

Step-by-step solution:

1. Wire 1 carries current upward. By the right-hand grip rule, its magnetic field circles the wire. At the position of wire 2 (beside it), the field points into the page (say).
2. Wire 2 also carries current upward, so it sits in the field of wire 1. Using Fleming's left-hand rule (First finger = field into the page, Second finger = current upward), the thumb (force) points toward wire 1.
3. By the same reasoning, wire 1 experiences a force toward wire 2.
4. The two forces point toward each other, so the wires attract.

The magnitude of the force per unit length is:

F/L = (μ₀ I₁ I₂) / (2πd)

where d is the separation between the wires.

Checking the options:

• A. Move in a circle: no, the force is along the line joining them.
• B. Repel: this happens only when currents are opposite.
• C. Remain stationary: no, there is a net force.
• D. Attract each other: correct.

Answer: D. attract each other

Exam tip: Remember "Same direction, Same side (attract); Opposite directions, Opposite motion (repel)." Note that this is the opposite of magnetic poles and electric charges, where like repels. For parallel currents, like currents attract.