Throughout the world, a huge effort is engaged in multimedia activities for educational products. This is particularly true in sciences where phenomenas are observed explained and used. Thus, multimedia through animation and interactivity proves all its potential. This paper describes the concept of a virtual lab developed at the LEG-EPFL (Electronics Laboratory of the Swiss Federal Institute of Technology). The main objective is to promote the complementarity with classical methods through the rapidity of the experiences, the possibility to visualize experiences impossible to see in the reality, the link between modelisation and reality. The difficulties of such a project will be presented and a first feed-back will be analyzed