The work function of copper is `4.57` eV. If radiation of 2500 Å is incident on copper, calculate the maximum velocity of photo electrons.

Explanation

`w = 4.57` eV `= 4.57xx1.6xx10^(-19)-7.312xx10^(-19)`J
Energy of incident photon is
`E=hv = (hc)/lambda`
`=(6.625xx10^(-34)xx3xx10^(8))/(2500xx10^(-10))=7.95xx10^(-19)`J
According to Einsteins photo electric equation,
`E = w + E_(k) = w + 1/2 mv^(2)`
`7.95 xx10^(-19)=7.312xx10^(-19)+1/2mv^(2)`
`1/2 mv^(2) = (7.95-7.312)10^(-19)=0.638xx10^(-19)`J
`v^(2)=2/mxx0.638xx10^(-19)=(2xx0.638xx10^(-19))/(9.1xx10^(-31))=1.402xx10^(11)`
`v=sqrt(1.402xx10^(11))=3.744xx10^(5)" ms"^(-1).`