I have a problem that ask for the minimum energy of a wave that we will use to see a particle of size .1 nm. I understand that I can not see a .1 nm particle with any wave length larger than .1 nm. I thought this would be easy and I would use De Broglis relation of electron waves. (f=E/h) or E=fh=hc/λ. Using this I get 12400eV..... this is the wrong answer. What the book says to do is use an eqn. "wavelength associated with a particle of mass M. it is: λ=hc/sqrt(2mc^2K) OR for my specific case: λ=1.226/sqrt(K) nm This second equation , if im correct, is getting the kinetic energy of the wavelength, not the total energy. I do not understand what I should be looking for in problems asking for energy of wavelengths to distinguish the use of the first eqn I presented Vs the second one. Any enlightenment on this area would be appreciated.