This article deals with an experimental proposal for studying physical phenomena associated to the trajectory of an electron beam submitted to electric and magnetic fields. The results of this work are being used in the discipline Structure of the Matter aiming that the students can understand basic principles involved in the construction of electron microscopes as the convergence of a divergent electron beam and the consequent formation of the cylindrical helix in the Busch helical method for the determination of the ratio e/m of the electron. Besides, this work shows how we can determine the intensity of the horizontal component of the Earth's magnetic field through the produced by the cylindrical helix.
specifies charge of eletrons; Earth's magnetic field; method of the helix of Busch; cathode rays
