All Problems

Constant Magnetic Field, Magnetics

Problem 3.256

Two long parallel wires of negligible resistance are connected at one end to a resistance RR and at the other end to a dc voltage source. The distance between the axes of the wires is η=20\eta=20 times greater than the cross-sectional radius of each wire. At what value of resistance RR does the resultant force of interaction between the wires turn into zero?

Reveal Answer
R≈μ0/ε0(ln⁡η)/π=0.36kΩR \approx \sqrt{\mu_{0} / \varepsilon_{0}}(\ln \eta) / \pi=0.36 \mathrm{k} \Omega
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