Hi guys, I am new to this forum and decided to join when i stubled upon a similar thread to the one i am about to post. The question i am pondering is this: In the question, the three lowest energy levels of an atom of the target material in the xray tube are shown and the question is: "What is the minimum Potential Difference at which the tube can operate if the transition from n=3 to n=1 is possible? Straight away i figured you just subtract n = 1 from n=3 and hey presto but my friend said he recalls the teacher saying something about you have to use the PD relating to the maximum transition, i.e. to allow the atom to be ionised entirely: 0 - (n=3). My thoughts on this is that the PD needed here is only enough to give the elctron enough energy to allow the electron to jump from n = 1 to n = 3. The atom's model is: n = 3 ----------------------- -11 x 10^3 n=2 ------------------------- -26 x 10^3 n=1 -------------------------- -98 X 10^3 Could anyone tell me if i am wrong and why? This question lead me on to wonder what can happen when an electron collides with an atom in general. If the energy of the incident electron is such that is slightly more than what is required to excite an electron to the next energy level , will the collision result in no energy being transferred to the atom? Or wil the energy transfer be such that an electron gets excited and the difference result in a phonon? In my notes regarding the line spectrum (characteristic spectrum) of atoms in an Xray tube it says "The line spectrum is the result of electron transistions within the atoms of the target material. The electrons which bombard the target are very energetic and are capable of knocking electrons out of deep-lying energy levels of the target atoms." So similarly does this suggest that if the incident high energy electron has more energy than what is required to eject a deep lying electron, the difference in energy could manufest as heat?