We investigate the electronic properties of InAs/GaAs quantum rings (QRs) in a magnetic field using an original effective potential model based on a single band kp -approximation with an energy dependent effective mass. We used two sets of geometrical parameters for the selfassembled QRs. The first is the experimentally proposed geometry; the second follows from the oscillator model due to the relation between the model parameters and the real sizes of the quantum objects. The energy of an electron in a magnetic field, calculated for each of the geometries, is compared with C-V experimental data. We show that the results of the calculation obtained for the second geometry fit the experimental data rather well. Interpretation of the recent C-V data given by W. Lei et al. (Appl. Phys. Lett. 96 (2010) 033111) on the basis of the oscillator model is discussed.