Why do the electrons move towards the point C under the magnetic field in the experiment about the charge to mass ratio of electrons?
The Lorentz force law(from Physics) tells us that a charged particle experiences a force in an area where there exists an electric or magnetic field and it is evident from Maxwell's theory also that charged particles(electromagnetic particles) could be deflected in a magnetic field. So, on applying a magnetic field, these electrons will be deflected by magnetic field. In this setup, the electron will move perpendicular to the magnetic field. Thus, the force on the electron is:
Hence, if greater is the magnitude of negative charge, greater is the interaction with magnetic field and greater is the deflection towards C.