Someone me how to do these my physics teacher does not teach us how to do these what formulas it belongs to & hands us homework

How does the space charge width change with forward and reverse bias? also, calculate the space charge width for a reverse bias of 4v on a silicon pn junction at t = 300k and doping concentrations of na = 5x1015cm-3 , nd = 5x 1016 cm-3 .

Calculate the work done by an external agent during an isothermal compression of 1.00 mol of oxygen from a volume of 22.4 l at 10∘c and 1.0 atm pressure to 16.8l

Need people build a dam to create a reservoir that supplies water a nearby city needs. describe two ways this action will likely affect the water cycle in the local environment. (5 points) worth 20 points