Mathematical and Physical Journal
for High Schools
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Problem P. 4550. (May 2013)

P. 4550. Two alike long, straight wires of diameter d, are at a distance of {D=50\,d}; their resistance is negligible and (L\ggD). One ends of the wires are connected through a battery of voltage U, and the other ends of the wires are connected through a resistor of resistance R. What is the value of R if the electric and magnetic forces exerted between the wires are equal?

(6 pont)

Deadline expired on June 10, 2013.

Sorry, the solution is available only in Hungarian. Google translation


\(\displaystyle R=\frac{1}{\pi} \sqrt{\frac{\mu_0}{\varepsilon_0}}\ln\frac{2D}{d}\approx 553\,\Omega.\)


17 students sent a solution.
6 points:Antalicz Balázs, Balogh Menyhért, Kollarics Sándor, Kovács 444 Áron, Olosz Balázs.
5 points:Sárvári Péter, Szabó 928 Attila, Váli Tamás.
4 points:1 student.
3 points:4 students.
2 points:1 student.
1 point:1 student.
0 point:2 students.

Problems in Physics of KöMaL, May 2013