posted by sonia .
A power line carries a current of 110 A at a location where the Earth's magnetic field has a magnitude of 0.37 Gauss (0.37·10-4 T) and points due north, very nearly parallel to the ground. Find the direction and magnitude of the magnetic force exerted on a 270 m length of the power line if the current in the line flows in the following directions:
horizontally toward the east
1.0989 N, upwards
horizontally toward the north
0 N, none of these; force is zero
QUESTION: How far away do you have to get from this power line, before the B field from the power line itself is about as small as the Earth's?
I could not figure out what formula to use to solve this..please help!