A straight wire AB of mass 40 g and length 50 cm is suspended by a pair of flexible leads in uniform magnetic field of magnitude 0.40 T as shown in the figure. The magnitude of the current required in the wire to remove the tension in the supporting leads is $\_\_\_\_$ A. (Take $g = 10 \mathrm {~m} \mathrm {~s} ^ { - 2 }$.)