A very long wire carrying current I is fixed along x-axis. Another parallel finite wire carrying a current in the opposite direction is kept at a distance d above the wire in xy plane. The second wire is free to move parallel to itself. The options available for its small displacements are in (i) +ve x direction (ii) +ve y direction (iii) +ve z direction Taking gravity in negative y direction, the nature of equilibrium of second wire is
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Question

A very long wire carrying current I is fixed along x-axis. Another parallel finite wire carrying a current in the opposite direction is kept at a distance d above the wire in xy plane. The second wire is free to move parallel to itself. The options available for its small displacements are in (i) +ve x direction (ii) +ve y direction (iii) +ve z direction Taking gravity in negative y direction, the nature of equilibrium of second wire is

Options

G1 Physics · Accepted Answer

For displacement along x the force balance is unchanged, giving neutral equilibrium. A small upward/downward y displacement changes magnetic repulsion relative to weight so the restoring tendency is stable in y. A z displacement makes the magnetic force drive the wire further away, so z is unstable. Hence B.