Electricity, Magnetism and Electromagnetism, Ch The Biot-Savart law and the fields of steady currents
Problem
A single-phase overhead line carries its current out along one conductor and back along the other. The two conductors run parallel and straight, d=4.0m apart, over a span of L=300m between towers, and at peak load each carries I=800A, the two currents being in opposite directions. Each conductor has a mass of 1.0kg per metre. Take g=9.81ms−2, treat each conductor as a long straight wire (the span is far longer than the separation), and ignore the sag of the cables and any field from other lines.
((a)) State, with a reason based on the field of one conductor at the other, whether the conductors attract or repel.
((b)) Estimate the magnitude of the magnetic force per unit length on one conductor.
((c)) Estimate the total magnetic force on one conductor over the span, and compare it with the weight of that length of conductor by giving the ratio (magnetic force)/(weight).