a.".. . For a moving electron, the electric field $E$ is equivalent to an additional magnetic field $\overrightarrow{B} = [\overrightarrow{\beta} \times \overrightarrow{E} ]$" (G. Bethe, E. Solipter. Quantum mechanics with one and two electrons, Moscow: Fizmatgiz, 1960). Determine, using this statement, the force acting on the magnetic moment of an electron in a hydrogen atom, if the electron) It's moving by circular orbit.