Mathematical and Physical Journal
for High Schools
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Problem P. 4389. (November 2011)

P. 4389. In order to make a flat coil, which have 200 turns, a piece of wire of negligible resistance is wound around a rectangular frame of area 50 cm2. The frame is rotated about one of the symmetry axis of the rectangle, which is in the plane of the rectangle. The frame is in magnetic field of induction 0,1 T, which is perpendicular to the axis of rotation. A bulb rated at 6,3 V, and 3 W, and a coil of resistance 10 \Omega, and of inductance 50 mH, are connected to the ends of the rotating coil in series.

a) What should the number of revolutions of the coil be, in order to gain 6.3 V voltage across the bulb.

b) At what phase angle does the current lag behind the voltage across the 50 mH coil?

(5 pont)

Deadline expired on December 12, 2011.

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

Megoldás. \(\displaystyle a)\) 26 Hz-nél.

\(\displaystyle b)\) \(\displaystyle 39{,}7^\circ.\)


32 students sent a solution.
5 points:Bingler Arnold, Bolgár Dániel, Filep Gábor, Kollarics Sándor, Koncz Gabriella, Kovács 444 Áron, Nagy Lajos, Nárai Ádám, Sárvári Péter, Virágh Anna.
4 points:Czipó Bence, Fülep Andrea , Garami Anna, Horváth Dániel, Jenei Márk, Juhász Péter, Laczkó Zoltán Balázs, Mázik László, Papp Roland, Pataki Bálint Ármin, Szabó 928 Attila, Szilágyi 585 Dezső, Tilk Bence, Ürge László, Váncsa Szilárd.
3 points:5 students.
2 points:2 students.

Problems in Physics of KöMaL, November 2011