a straight wire of length L carrying current I stays suspended horizontally in mid air in a region of uniform magnetic field B. the linear mass density of wire is lambda . obtain the magnitude and direction of magnetic field..

Force on the current carrying wire, F = BIl 

Weight of the current carrying wire, F' = mg

where m = λl

For suspension,

F =F'

⇒ λlg = BIl

⇒B = λg/I

The direction of the magnetic field perpendicular to the length of the conductor can be found out using Fleming's left hand rule.