Question

Steel and iron are often 'galvanized', or coated with a thin layer of zinc metal to prevent corrosion (iron rusts but zinc does not). What is the longest wavelength of light (in nm) that can eject electrons from zinc metal? (i.e. assume the electron's kinetic energy is very close to zero.) The work function of zinc = 4.3 eV and 1 electron-volt (eV) = 1.602*10^-19 J.

Answer 1

Energy supplided to metal = work function + Kinectic energy of ejected electron

E = 4.3 eV + 0

= 4.3 eV = 4.3 x 1.602 x 10^ -19 J = 6.8886 x 10^ -19 J

we now use E = h c / lamda     where lamda is wavelength in m

6.8886 x 10^ -19 = ( 6.625 x 10^ -34 x 3 x 10^ 8) / lamda

lamda = 2.8852 x 10^ -7 m = 288.5 x 10^ -9 m = 288.5 nm    ( since 1nm = 10^ -9 m )

hence waveleggth corresponding to eject electron form metal is 288.5 nm