RE-NEET 2026 Physics Magnetic Forces MCQ Question
Two infinitely long parallel conducting wires A and B carry currents I and 2I, respectively, in the same direction. The wire A has uniform mass per unit length λ and lies on an insulated floor. The wire B is kept fixed at a height h above the floor. The minimum magnitude of h so that the wire A does not rise from the floor is : [g is the acceleration due to gravity and μ₀ is the permeability of free space.]
μ₀I²/πλg
2μ₀I²/πλg
4μ₀I²/πλg
μ₀I²/2πλg
Correct Answer
Detailed Explanation
The magnetic force per unit length between two parallel currents is given by F = μ₀I₁I₂/2πd. For equilibrium, this force must balance the gravitational force λg. Solving for h gives h = μ₀I²/πλg.
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