0A parallel Plate Capacitor's Capacitance can be changed. But How? Let's explore the following options:-
1. Applied Battery Voltage V can be changed
2. Area of plates can be changed so that more charge can be accumulated
3. Distance between the plates can be changed
4. The Dielectric material between the plates can be changed.
Option 1: Voltage Change to change Capacitor: We increase the applied voltage V, and the Capacitor gains Charge (Q). As the Capacitor is being charged the charge on the Capacitor is increasing and therefore the battery has to work very hard to push the charge on the plate because the charge accumulated on the plate will repel the new charge coming from the battery. At some point, the repulsion between the charges reaches a point where the battery is not able to push any more charge. Alternatively, we can say that potential on plates becomes equal to Battery emf so that no further flow of charges. So if one studies Option 1 closely, one can say that Voltage change changes the Charge on the Capacitor. It does not change the Capacitor. This is an important concept.
Option 2: Change in Area of Plates: Capacitance of a Parallel Plate Capacitor is directly proportional to Area. Higher the area of plates is higher the Capacitance. So size ( Area ) matters. A bigger area means that charges on each plate can spread out more. The charges on the negatively charged plate will spread out more if more area is available. This spreading happens because of the repulsion of like charges on a parallel plate.
Option 3: Change in distance between plates: Capacitance of a Parallel Plate Capacitor is inversely proportional to d -the distance between the plates. More is the distance between the plates lower is the plates. So again size ( distance between plates is Size ) matters. A closer distance between plates means a very good force of attraction between oppositely charged plates and hence higher capacitance. If one reduces the distance between the plates to a very low value, there is a danger of the dielectric between the two plates breaking down. So there is a limit to which one can reduce the distance between the plates and hence one cannot attain any amount of capacitance just by reducing the distance between the plates.
Option 4: Change in Material ( aka Dielectric) between Parallel Plates: If we change the Dielectric between the Capacitor; the electric field between the plates changes and the Potential difference also changes. This is because of the Polarisation of the dielectric. Polarisation implies the separation of charge within an atom or molecule. One should read about the Polarisation of Dielectric in detail. The charge generated on Dielectric produces an Electric field which opposes the Electric Field between the plates. So-net Electric field is lowered between the plates by the introduction of Dielectric. Thus a lowered electric field results in lowered potential difference. A lower potential difference for the same charge implies higher Capacitance. If you add a Dielectric with higher Dielectric constant, the Capacitance goes up.
