You may have noticed a type of track lighting in museums or stores with modern decor called "cable track lighting." Bare power supply wires, 60 mm apart, are strung across a room up to 6 meters and are connected to a 12 volt source (usually a step-down transformer). Halogen lamps are then clamped to the bare wires. A pair of wires can typicaly handle a maximum wattage of 350 watts.
What is the force between the long wires?
How does the magnetic field ate one wire due to the other compare with the earths magnetic field?