I am trying to calculate the minimum potential required to view a K alpha line for a certain element: After some algebra I have E = hc*R_inf*(Z - 1)^2 * (1 - 1/n^2) Why must n->inf in order for me to view the K alpha line for the element? I did the problem and I just used n = 2, because my book says the lowest frequency line corresponds to the lowest energy transition, n = 2 to n = 1. Then it goes on to say that this line is the K alpha line, so I don't get why they would use infinity. I must be missing something vital. If anyone can help it would be great.