Hi all, exams in a few weeks and having a bit of trouble understanding the characteristics of plasmas/sheaths. E.g. the following question from a sample paper "Describe the characteristics of the sheath that forms at the boundaries of confined plasma. In your answer state what is meant by the bohm velocity, explain what a pre-sheath is and why it is needed and why the sheath is dark. Discuss RF sheaths for the case where the RF frequency is less than the electron plasma frequency and greater than the ion plasma frequency. In your answer state when the electrons are able to flow ad describe the equivalent circuit of the sheath." I kind of understand the pre-sheath and bohm velocity, and very slightly the "darkness" of the sheath but not sure about the rest. Any help at all would be greatly appreciated!!!