Now If I consider a parallel plate capacitor connected across a battery then ,
force(f) between the plates should not be proportional to distance(d) (that's what I think)
as force due to plate on other=$q\sigma/\epsilon_0$ where $\sigma $would be the charge density and q be the charge on other plate.
But my text says it's inversely proportional to distance . Now what I think is that what I did above may be correct for only an isolated capacitor but given is connected across terminals; If so then how can I derive it mathematically that : $f\alpha d^-2$