Mathematical and Physical Journal
for High Schools
Issued by the MATFUND Foundation
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# Problem P. 4162. (April 2009)

P. 4162. A magnetized needle can swing horizontally inside a solenoid whose symmetry axis is horizontal. The length of the solenoid is 25 cm, and the number of its turns is 100. When there is no current in the solenoid the needle makes 10 total swings in each minute due to the magnetic field of the Earth. Now the solenoid is placed such, that its symmetry axis is perpendicular to the magnetic meridian. The needle makes 51 swings in each minute when the current in the solenoid is 1 A.

a) What is the horizontal component of the magnetic field of the Earth at the location of the experiment?

b) How many swings does the needle make if the direction of the current in the solenoid is changed? (Its magnitude remains the same.)

(4 pont)

Deadline expired on May 11, 2009.

### Statistics:

 14 students sent a solution. 4 points: Boros Csanád Örs, Emroz Khan, Garaguly Gergő, Maknics András, Szabó 928 Attila, Szédelyi Roland, Zelei Kristóf. 3 points: Hartstein Máté, Laczkó Zoltán Balázs, Lovas Lia Izabella, Najbauer Eszter Éva. 2 points: 1 student. 1 point: 2 students.

Problems in Physics of KöMaL, April 2009