1. The problem statement, all variables and given/known data A glass prism is used to launch an evanescent wave along a glass-air interface. What is the minimum incident angle to excite the evanescent wave? 2. Relevant equations 3. The attempt at a solution I dont understand what the question is asking for. I have read and reread the section in my book about evanescent waves it doesn't say anything about this? what does the question mean by "excite"?