After the third semester is completed you should choose your advisor among associate or full professors and start working on your dissertation. During your final semester, if you pass all courses, collect enough ECTS points, and your dissertation is completed you can defend it. During the defence you have to present an oral talk about your dissertation, address questions related to your dissertation as well as general knowledge of physics. If you are successful you receive your B.Sc. degree in physics and you can relax. Enjoy!