Could anyone explain why the intensity of the electric field between plates of a charged capacitor is constant? Moreover, the varying the distance between plates doesn't change the electric field intensity - that's weird, because the electric field is defined as the force acting on a unit charge, and the force according to Coulomb law certainly does depend on the distance between the charges.
So it's reasonable to expect that placing two plates further apart would result in a lower electric field intensity (or, lower force experienced by a unit charge placed between the plates), but that's not the case (for some reason).
See example 4.2 if you need technical details.
Let's say the value of charge, not potential, is fixed on both plates. Does the electric field insensity change with the distance between the plates? The answer has to be 'no', because doubling the distance between plates of a capacitor doubles the voltage across them (and $V=Ed$). And if the electric field intensity remains constant (it's just force acting on unit charge), then the force acting on the test charge will be the same no matter how far apart the plates are.