The work function of sodium metal is $4.41\times {10}^{-19}J$ . If photons of wavelength 300 nm are incident on the metal. The kinetic energy of ejected electrons will be   $\_\_\_\_\_\times {10}^{-21}J(h=6.63\times {10}^{-34}J.\sec ,c=3\times {10}^{8}m/\sec )$