A wire AB is carrying a steady current of 12 A and is lying on the table. Another wire CD carrying 5A is held directly above AB at a height of 1 mm. Find the mass per unit length of the wire CD so that it remains suspended at its position when left free. Give the direction of the current flowing in CD with respect to that in AB.
[Take the value of g = 10 ms–2]

Current carried by wire AB= 12 A

Current carried by CD = 5 A

 i) The current-carrying conductors will repel each other if the direction of current along both the conductor is the same.

 ii) When current along the conductors is flowing in the same direction, then the wires will attract each other.

When CD remains suspended above AB, 

where r is the distance between the wires.

Therefore, 

The direction of the current in CD should be opposite to the direction of the current in AB.