A straight wire of mass 200 g and length 1.5 m carries a current of 2 A. It is suspend in mid-air by a uniform horizontal magnetic field B (Figure). What is the magnitude of the magnetic field ?

Explanation

From Eq. (4) we find that there is upward force F, of magnitude I/B . For minair suspension, this must be balanced by the force due to gravity : mg= I/B
`B = (mg)/(Il) = (0.2 xx 9.8)/(2 xx 1.5) = 0.65 T`