The work function of a metal is 4.2eV. If the radiation of `2000Å` falls on the metal, find the kinetic energy of the metal

Explanation

`"Work function "E_(0)=hv_(0)=4.2eV`
`=4.2xx1.602xx10^(-19)J=6.7284xx10^(-19)J`
`"Energy (E) is given as "`
`E=hv=(hc)/(lambda)=(6.625xx10^(-34)Jxx3.0xx10^(8)ms^(-1))/(2000xx10^(-10)m)`
`"Threshold energy, "E_(0)=6.7284xx10^(-19)J`
`"Kinetic energy, "KE=E-E_(0)`
`=[9.939xx10^(-19)J-6.728xx10^(-19)J]`
`=3.211xx10^(-19)J`