  The ballistic motion of carriers of graphene in an orthogonal electromagnetic
field is investigated to explain Hall conductance of graphene under
experimental conditions. With the electrical field, all electronic eigen-states
have the same expectation value of the velocity operator, or classically, all
carriers move in cycloids with the same average velocity. The magnitude of this
velocity is just appropriate to generate the quantized Hall conductance which
is in turn exactly independent of the external field. Electrical field changes
each Landau level into a bundle of energies, whose overlap in large fields
destroys the quantized Hall conductance. As the electrical field tends to the
critical point, Landau level expansion occurs. As a result, saturation of the
Hall conductance may be observed.
