The work function for cesium atom is 1.9 eV.
Calculate the threshold wavelength.

Explanation

Work function of cesium `(w_(0))=hv_(0)=1.9eV`
`therefore`Threshold frequency, `v_(0)=(1.9eV)/(h)=(1.9xx1.602xx10^(-19))/(6.626xx10^(-34)J*s)`
or, `v_(0)=4.59xx10^(14)s^(-1)" "[because 1eV=1.602xx10^(-19)J]`
Again, threshold wavelength `(lamda_(0))=c//v_(0)`
`=(3xx10^(8)m*s^(-1))/(4.59xx10^(14)s^(-1))=6.536xx10^(-7)m`
Thus threshold wavelength of cesium`=6.536xx10^(-7)m=654xx10^(-9)m=654nm`