Abstract: This research studies the distribution of the restricted ion on the surface of the sample (PMMA) Poly-Methyl Methacrylate by irradiating it with an ion beam inside Focusing Ion Beam device (FIB). Using the charged disc approach, the mathematical description for the process of charging restricted ions on the surface of the sample has been provided. Although, the theoretical formulation has been provided depending on simple ideas of electricity, however, it provided fairly consistent results with practical results. In the current work, a theoretical relationship was derived to help researchers overcome the mirror effect for the first time.