Two long parallel conductors separated by a certain distance 'd' and carrying steady currents \( I_1 \) and \( I_2 \) are shown in figures. Choose the correct statement.
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → In figure-1 conductors attract each other and in figure-2 they repel each other
Each conductor sits in the magnetic field of the other, and the force on it is \( \vec{F} = I\,\vec{l}\times\vec{B} \). The result is that parallel currents attract and antiparallel currents repel, with force per unit length
\( \displaystyle \frac{F}{l} = \frac{\mu_0 I_1 I_2}{2\pi d} \)
Figure-1: \( I_1 \) and \( I_2 \) both flow upward (same direction), so the conductors attract each other.
Figure-2: \( I_1 \) flows upward and \( I_2 \) downward (opposite directions), so the conductors repel each other.
NCERT (2026-27):
Force Between Two Parallel Currents, the Ampere – “… We have seen from above that currents flowing in the same direction attract each other. One can show that oppositely directed currents repel each other. Thus, Parallel currents attract, and antiparallel currents repel.”