The photoelctric effect work function for a metal is 4.2 eV. If the stopping potential is 3V, find the threshold wavelength and the maximum kinetic energy of emitted electrons.

Explanation

Data: `e=1.6 xx 10^(-19) C, c=3 xx 10^(8) m//s, h=6.63 xx 10^(-34) J.s, Phi=4.2 eV = 4.2 xx 1.6 xx 10^(-19) J =6.72 xx 10^(-19) J, V_(s) = 3V`
The threshold wavelength,
`lambda_(0) = (hc)/Phi`
`=((6.63 xx 10^(-34))(3 xx 10^(8)))/(6.72 xx 10^(-19))`
`=(19.89)/(6.72) xx 10^(-7) = 2.960 xx 10^(-7) m = 2960 Å`
The maximum kinetic energy of emitted electrons, `KE_("max")`
`=eV_(s) = (1.6 xx 10^(-19))(3) = 4.8 xx 10^(-19)` J