“Simulation” is a word that might be familiar to everybody. Its meaning is so expanded in all sectors (medicine, education, biology, engineering, psychology...), that the introduction of this paperwork will mainly focus only on computer simulations subject. To better understand what a computer simulation is, the most suitable and simple definitions are below: “The technique of representing the real world by a computer program”; "a simulation should imitate the internal processes and not merely the results of the thing being simulated"; “is a technique to perform tests using a model written in software” Why do we use computer simulations? The answer to this question may seem very long, but the main reasons for using simulations are easy to find, although they depend on what area we are in: Business simulations: Modern business has to stay competitive by keeping development and training costs and times to a minimum, while still keeping high levels of quality for both. Modeling and simulation of systems can provide solutions for product development and personnel training without the costs usually associated with these. In other words: computer simulations save time and money, and they are as reliable as real world tests. Education simulations: They provide the students with one intermediate space, which joins the reality with the models or theories. In addition, simulations allow interactive manipulation of the models, that will facilitate the acquirement of knowledge of the students. Obviously the subject of this work is to program and to study an example of “educational simulation”. More specifically, the simulation we work on is an interactive simulation, which intends to provide the students with a tool they can play with. The students can better understand the mathematical model used to explain the phenomena under study, because they can check and observe, in an interactive way, the reality the model represents. Our Applet simulation is drawn on a 2D projection of a 3D interactive graph representing two plane waves, one electric and the other magnetic, with z axe as their direction of propagation. It is an interactive Applet because the users can change the values of the wave equations through sliders, buttons and combo boxes.