A new and simple approach aimed at understanding the nature of the radial electric field in some types of tokamak plasmas is presented. It is shown that the radial electric field at some point on a magnetic surface in a tokamak plasma can be divided physically into two parts. The first part is related to a very small difference between densities of electrons and ions of two component plasmas on a magnetic surface in the corotating frame. The second part is related to toroidal rotations of current layers on magnetic surfaces. A new integral equation is calculated. The efficiency of this approach is shown by means of an illustrative example of a Tore-Supra experiment.