The cross-section of twisted pair
The cross-section of each and every strand of the twisted pair is π/4 square mm. A 10-km length of this type of material, with two strands per pair will have a volume of 2π/4 × 10-2 m3. This volume is around 15,708 cm3. With specific gravity of 9.0, each local loop has mass of 141 kg. The phone company therefore owns1.4 × 109 kg of copper. At 3 dollars each, copper is worth about 4.2 billion dollars.