# 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