• # question_answer 48) A photon materializes into an electron-positron pair. The kinetic energy of the electron is found to be $0.19\text{ }MeV$. What was the energy of the photon? A)  $0.38\text{ }MeV$                   B)  $0.70\text{ }MeV$C)  $1.40\text{ }MeV$                   D)  None

Conservation of Energy, $Photon\to {{e}^{+}}+{{e}^{-}}+energy$ ${{E}_{P}}={{E}_{r{{e}^{+}}}}+{{E}_{r{{e}^{-}}}}+K.E.$ of both ${{e}^{-}}+{{e}^{+}}$ We know that  rest mass energy of ${{e}^{+}}+{{e}^{-}}$is.$5\text{ }MeV$ Hence ${{E}_{p}}=.5+.5+.19\times 2=1.40\,MeV$