This research investigates the influence of computer simulations (virtual experiments) on one hand and real experiments on the other hand on the conceptual understanding of electrical charging. The investigated sample consists of students in the second year (10th grade) of three gymnasiums in Macedonia. There were two experimental groups and one control group. In one of the experimental groups, called Sim group, the instruction was realized by means of computer simulations. In the other experimental group, called Real group, the instruction was realized by means of real experiments. The difference between pre-test results and post-test results revel that the approaches used in experimental groups give more quality knowledge and skills than the one in the control group. The results in the Real group and Sim group are very similar. There are slight differences caused by the different features of the two approaches. Some differences occur based on the feature difference between real experiments and computer simulations.