$1$Scientists are now able to make photoelectric cells that can detect with near$-$perfect efficiency all the photo$-$ejected electrons from a metal surface. $($A$)$ sodium metal is placed in such a cell and is irradiated with $300nm$ light the maximum kinetic energy of the ejected electrons is $2\mathrm{.}313eV.($A$)$ Calculate the work function of the metal $($Joule units$).($B$)$ If an incident light source is maintained at $60\mathrm{.}0$ Watts over all frequencies, calculate the photocurrent $($in Ampere units$)$ at $800nm,600nm,400nm.$