Mathematical and Physical Journal
for High Schools
Issued by the MATFUND Foundation
 Already signed up? New to KöMaL?

# Problem P. 4692. (December 2014)

P. 4692. A straight coil of length $\displaystyle L=20$ cm, of cross-section of $\displaystyle A=12~\rm cm^2$ and of number of turns $\displaystyle N=400$ can rotate in the horizontal plane along a vertical axle through its centre. The coil is in uniform horizontal magnetic field of induction $\displaystyle B=0.05$ T. Initially the coil is perpendicular to the magnetic induction, and there are two unstretched springs attached to both of its ends, as shown in the figure. The other ends of the springs are also fixed and initially the springs are perpendicular to the coil. The spring constant of the springs is $\displaystyle D=24$ N/m, and their length is $\displaystyle \ell_0=20$ cm.

After the switch is turned on, there will be current in the coil. What is the current in the coil if the coil will be in equilibrium after turning an angle of $\displaystyle \alpha=60^\circ$?

(6 pont)

Deadline expired on January 12, 2015.

### Statistics:

 34 students sent a solution. 6 points: Balogh Menyhért, Blum Balázs, Bugár 123 Dávid, Csorba Benjámin, Csurgai-Horváth Bálint, Di Giovanni Márk, Fehér Balázs, Fekete Panna, Forrai Botond, Holczer András, Kasza Bence, Kovács Péter Tamás, Lőrincz Zoltán, Mándoki László, Marosvári Kristóf, Olosz Balázs, Sal Kristóf, Trócsányi Péter. 5 points: Büki Máté, Fülöp Erik, Gróf Tamás, Kaposvári Péter, Körtefái Dóra, Szántó Benedek, Szentivánszki Soma . 4 points: 3 students. 3 points: 2 students. 2 points: 2 students. 1 point: 1 student. 0 point: 1 student.

Problems in Physics of KöMaL, December 2014