 Mathematical and Physical Journal
for High Schools
Issued by the MATFUND Foundation
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# Problem P. 4670. (October 2014)

P. 4670. The diameter of a solenoid of length $\displaystyle \ell=2$ m is $\displaystyle D=2$ cm. The solenoid has $\displaystyle N=2000$ turns, its axis is vertical and an upward direct current of $\displaystyle I=10$ A flows in it. (The circuit is closed far away from the coil.) Electrons are projected towards the axis of the coil perpendicularly to it, at an initial speed of $\displaystyle v=2.5\cdot10^6$ m/s. What is the radius of the paths of the electrons at the point which is at a distance of $\displaystyle d=2$ cm from the turns of the coil.

(6 pont)

Deadline expired on November 10, 2014.

### Statistics:

 10 students sent a solution. 6 points: Olosz Balázs, Sal Kristóf. 5 points: Berta Dénes, Büki Máté, Orosz Bálint, Öreg Botond. 4 points: 2 students. 3 points: 1 student. 2 points: 1 student.

Problems in Physics of KöMaL, October 2014