A long silicon pn junction solar cell has the same parameters as described in Problem $14\mathrm{.}10.$ The generated photocurrent in the cell is IL $120$ mA$.$ Determine the $($a$)$ open$-$circuit voltage, $($b$)$ the voltage across the junction that will produce a total solar cell current of I $100$ mA$,($c$)$ the maximum power output of the solar cell, and $($d$)$ the external load resistance that will produce the maximum power.