The effective medium approximation is one of the most popular approximations used for calculating the effective coefficients of linear composite media. When the same approach is applied to the case of power-law nonlinear composite media the obtained expression contains a function whose values are unknown. In order to determine the form of this function and to calculate some coefficients related to it, we calculate the electric field for the case of a single inclusion. The numerical solution is based on the relaxation method for solving differential equations, but involves some modifications due to the nonlinearity. After the solution of the differential equation the function and the coefficients are calculated and examined. The results differ considerably from those obtained earlier by simple approximations.