Explanation:
It is given that,
Length of the wire, L = 2.1 m
Current, I = 5.1 A
Mass of the wire, m = 0.2 kg
Let B is the magnitude of the magnetic field necessary to have this wire "float" in the Earth's gravitational field such that,
[tex]F_g=F_m[/tex]
[tex]mg=ILB[/tex]
[tex]B=\dfrac{mg}{IL}[/tex]
[tex]B=\dfrac{0.2\times 9.8}{5.1\times 2.1}[/tex]
B = 0.18 T
The direction of magnetic field is given by Fleming's left hand rule. Here, the magnetic field is in +x direction.