Mathematical and Physical Journal
for High Schools
Issued by the MATFUND Foundation
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# Problem P. 4032. (December 2007)

P. 4032. A uniform metal disc is rotated about an axle, which goes through its centre and which is perpendicular to it. The disc is in uniform magnetic field, the magnetic induction is parallel to the axis of rotation. Usually electromotive force is induced between the rim of the disc and its axle. Though if we are clever we can rotate the disc in such way that no e.m.f. induced between the rim and the axle. How should we rotate the disc if the magnetic induction at the disc is 10-8 T.

(5 pont)

Deadline expired on January 11, 2008.

### Statistics:

 31 students sent a solution. 5 points: Almási 270 Gábor András, Berta Katalin, Csige Péter, Deák Zsolt, Demeter Dániel, Földes Imre, Földes Tamás, Guszejnov Dávid, Harsányi Szabolcs, Hlatky Dávid, Kalina Kende, Kovács 235 Gábor, Kovács 915 István, Krämer Zsolt, Kuzmich Ambrus, Lovas Lia Izabella, Ölvedi Tibor, Papp Ádám, Rárósi Dávid, Szabó Gábor Balázs, Szolnoki Lénárd, Szük Dániel, Tolner Ferenc, Tószegi Károly, Tóth 123 László, Török 125 Csaba, Túri Attila. 4 points: Hartstein Máté. 3 points: 1 student. 1 point: 2 students.

Problems in Physics of KöMaL, December 2007