The Force is strong with this one
Two long parallel wires of negligible resistance are connected at one end to a resistance R and at the other end to a DC voltage source. The distance between the axes of the wires is n = 20 times greater than the cross-sectional radius of each wire. At what value of resistance R does the resultant force of interaction between the wires turn into zero?
Problem from "Problems in General Physics" by IE Irodov.
Answer in kilo-ohms.