Investigating the deflection of electrons in electrical and magnetic fields

The experiment P3.8.5.1 investigates the deflection of electrons in electric and magnetic fields. For different anode voltages U_A, the beam path of the electrons is observed when the deflection voltage U_P at the plate capacitor is varied. Additionally, the electrons are deflected in the magnetic field of the Helmholtz coils by varying the coil current I. The point at which the electron beam emerges from the fluorescent screen gives us the radius R of the orbit. When we insert the anode voltage in the following equation, we can obtain an experimental value for the specific electron charge

whereby the magnetic field B is calculated from the current I.