Exam preparations

I studied quite a bit over circuits and light and sound energy. I think my understanding of circuits is good. However, I need to really review on light and sound energy as I'm unclear about quite a lot. For example, I need to review how to use the periodic table properly. To be honest, I'm worried about the exams because I think I won't do so well. This is why i'm giving my self these 30 minute study periods every weekend.