Derive an expression for capacitance of a paralle plate capacitor

Explanation

Consider two parallel plates P and Q each of area a and separated by a distance d in air. Let plate P has surface desity `+sigma` and plate Q has surface charge density `-sigma` and plate Q has surface charge density `-sigma`
The electric field between the plates ` E = (sigma)/(epsilon_(o)) = (q//A)/(epsilon_(o)`
`E= (q)/(Aepsilon_(o)0`,
But potentail difference plates , v = Ed
now capacitanece, `C= (q)/(V)= (q)/(Ed)= (q)/((q)/(Aepsilon_(0))xxd)`
`C - (epsilon_(0)A)/(d)`