Given data: The length of the rod is
a)
Since, the magnetic field is equal and opposite to the weight of the wire.
The magnetic field is given as,
Where, the length of the rod is
By substituting the values in the above equation, we get
Thus, the magnetic field should be set up
b)
Since, the direction of current is reversed.
The total tension in the wire is given as,
Where, the total tension in the wire is
By substituting the given values in the above expression, we get
Thus, the total tension in the wire is