Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): Two long parallel wires carrying currents in the same direction attract each other.
Reason (R): The magnitude of the magnetic field of a long straight current-carrying wire is inversely proportional to the distance from the wire.
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Both (A) and (R) are correct but (R) is NOT the correct explanation of (A).
Assertion (A) Two long parallel wires carrying currents in the same direction attract each other. — True. Currents in the same direction attract. Currents in opposite directions repel.
Reason (R) The magnitude of the magnetic field of a long straight current-carrying wire is inversely proportional to the distance from the wire. — True. The field of a long straight wire is \( B=\mu_0I/2\pi d \), so \( B\propto 1/d \).
Why Reason (R) does not explain Assertion (A)?
R tells only how strong the field of one wire is at the other wire. It says nothing about the direction of the force.
The attraction comes from the force \( I_bLB_a \) on wire b in the field of wire a. When the currents are in the same direction, this force points towards wire a.
NCERT (2026-27):
Force Between Two Parallel Currents, the Ampere – “The conductor ‘b’ carrying a current Ib will experience a sideways force due to the field Ba. The direction of this force is towards the conductor ‘a’ …”
Force Between Two Parallel Currents, the Ampere – “Parallel currents attract, and antiparallel currents repel.”
Ampere’s Circuital Law – “… The field is directly proportional to the current and inversely proportional to the distance from the (infinitely long) current source.”