College Physics 10th Edition by Raymond Serway,Chris Vuille

Exercise 59

An electron is moving at a speed of 1.0 × 10 4 m/s in a circular path of radius 2.0 cm inside a solenoid. The magnetic field of the solenoid is perpendicular to the plane of the electron's path. Find (a) the strength of the magnetic field inside the solenoid and (b) the current in the solenoid if it has 25 turns per centimeter.