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

Explanation

Force experienced by wire `F_m = BIl` (due to map field)
The force due to gravity, `F_g = mg`
`mg = BI// rArr B = mg//il = (0.2 xx 9.8)/(2xx1.5) = 0.657 T`
[Earth's mag. Field `4xx 10^(-5)T` is negligibel]