Light of Intensity $10^{-5}W/m^2$ falls on a sodium photo-cell of surface area $2\: cm^2$ .Assuming that the top 5 layers of sodium absorb the incident energy, estimate time required for photoelectric emission in the wave – picture of radiation.( Effective atomic area of a sodium atom = $10^{-20}m^2$ )

Question

$\begin {array} {1 1} (a)\;0.607\: years & \quad (b)\;0.507\: years \\ (c)\;9\: months & \quad (d)\;1208 \: days \end {array}$