K.E. \(=1 / 2 m v^{2}=h f-h f_{0}\)
\(K . E=h\left(f-f_{o}\right)\)
\(=6.6 \times 10^{34}\left(8 \times 10^{15}-4.5 \times 10^{15}\right)\)
\(6.6 \times 10^{-34} \times 10^{15}(8-4.5)\)
\(6.6 \times 10^{-34+15} \times 3.5=23.1 \times 10^{-19} J\)
\(1 eV =1.6 \times 10^{-19} J\)
\(x e V=23.1 \times 10^{-19} J\)
\(x=\frac{23.1 \times 10^{-14}}{1.6 \times 10^{-14}}=14.44 eV\)