The attractive force decreases with the distance in the same proportion as light, which, we saw a little while ago, decreases in intensity as the square of the distance increases.
As the transmission length reaches a certain distance, DC transmission becomes economically attractive over ac.
当输电距离足够长时，直流输电的经济性将优于交流输电。
3
One study found that oxytocin led men in monogamous relationships to keep a greater distance between themselves and an attractive woman during an initial encounter.