[tex]Dane:\\f = 1,2\cdot10^{15} \ Hz\\W = 2,5 \ eV = 2,5\cdot1,6\cdot10^{-19} \ J = 4\cdot10^{-19} \ J\\1 \ eV = 1,6\cdot10^{-19} \ J\\h = 6,63\cdot10^{-34} \ Js\\Szukane:\\E_{k}=?\\\\Rozwiazanie\\\\E_{f} = h\cdot f\\\\E_{f} = 6,63\cdot10^{-34} \ Js\cdot1,2\cdot10^{15} \ Hz\\\\E_{f} = 7,96\cdot10^{-19} \ J\\\\\\E_{f} = W + E_{k}\\\\E_{k} = E_{f}-W\\\\E_{k} = 7,96\cdot10^{-19} \ J - 4\cdot10^{-19} \ J\\\\\boxed{E_{k} = 3,96\cdot10^{-19} \ J}[/tex]
