[SOLVED] recoil energy 1. The problem statement, all variables and given/known data Calculate the recoil energy and velocity of a hydrogen atom in a transition from the state « = 4 to the state AT = 1, in which a photon is emitted. 2. Relevant equations E=-13.5/n^2 E=mc^2/sqrt(1-v^2/c^2) 3. The attempt at a solution |E4-E1|=13.6-13.6/16 eV = 12.75 eV Invoking the total energy, Before emission mc^2 = E recoil + |E4-E1|=> E recoil = 1.50 *10^-10 J I couldn't get the correct answer. I wonder what is wrong? am I understanding the meaning of recoil energy wrongly?