A horizontal conducting rod of length 0.45 m and mass 60 g is suspended by two vertical wires and carries 5.0 A. Which option correctly gives (i) the magnetic field normal to the rod that makes the wire tensions zero and (ii) the total tension if the current is reversed while the field is unchanged? Take g=9.8 m/s².
Options

Question

A horizontal conducting rod of length 0.45 m and mass 60 g is suspended by two vertical wires and carries 5.0 A. Which option correctly gives (i) the magnetic field normal to the rod that makes the wire tensions zero and (ii) the total tension if the current is reversed while the field is unchanged? Take g=9.8 m/s².

Options

G1 Physics · Accepted Answer

For zero tension, magnetic force ILB balances mg: B=mg/(IL)=0.06×9.8/(5×0.45)≈0.26 T, oriented for upward force. Reversing current makes magnetic force downward with magnitude mg, so total support tension is mg+mg=2mg=1.176 N. Hence A.