Question

A power line 10 meter high carries a current 200 amperes .Find the magnetic field of the wire at ground?

Answer 1

Wonder where the return current is flowing? Ground?

Ok, assuming power can be transmitted by only one wire, then Ampere's law applies

INT B.ds=mu*I
B*2Pi*10=mu*200
solve for B

Answer 2

4*10^-6