  Energy spectrum of fractional quantum Hall (FQH) states is composed of single
electron energy (Landau energy) neglecting the Coulomb interactions between
electrons, classical Coulomb energy and the quantum energy via quantum
transitions. Herein, the sum of the Landau energy and the classical Coulomb
energy depends upon the value of the filling factor continuously. However, the
quantum transition energy discontinuously depends upon the value of the filling
factor. This discontinuity yields energy gaps in many stable FQH states. The
energy gaps for specific filling factors produce the precise confinement of
Hall resistance.
  A new experiment is considered as follows; the magnetic strength is fixed to
the value to confine the Hall resistance at the filling factor of 2/3 as an
example. Moreover the magnetic modulation with frequency f is applied to the
system. The frequency dependence of the diagonal resistance is measured. Then,
it is shown in this paper that the diagonal resistance varies drastically at
some frequency value f0. We clarify the following relation between this value
f0 and the magnetic strength width dB of Hall plateaus as f0 = e dB / (4 Pi m),
where -e is the charge of electron, Pi =3.141592, and m is the mass of
electron.
