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

Explanation

Work function `E_(0) = h v_(0) = 4.2 eV`
`= 4.2 xx 1.602 xx 10^(-9) J = 6.7284 xx 10^(-19) J`
Energy (E) is given as
`E = hv = (hc)/(lambda) = (6.625 xx 10^(-34) J xx 3.0 xx 10^(8) ms^(-1))/(2000 xx 10^(-10)m)`
Threshold energy, `E_(0) = 6.7284 xx 10^(-19)J`
Kinetic energy `KE = E-E_(0)`
`= [9.939 xx 10^(-19)J - 6.728 xx 10^(-19)J]`
`= 3.211 xx 10^(-19)J`