What three factors affect the stored charge in a capacitor?

The correct answer highlights the role of the dielectric between the plates of a capacitor in determining the stored charge. The primary function of a dielectric material is to increase the capacitor's ability to store electrical energy. When a dielectric is inserted between the capacitor plates, it reduces the electric field strength for a given voltage, allowing the capacitor to store more charge at the same voltage compared to an air gap or vacuum. This enhancement can be quantified by the dielectric constant of the material, which is key in understanding how capacitors function.

The effective area of the plates is indeed crucial, as a larger plate area allows more charge to be stored, while the voltage rating of the capacitor indicates the maximum voltage that can be applied without causing failure but does not directly influence the charge stored at a specific voltage. Similarly, the type of circuit connected can affect the overall performance and behavior of the capacitor in that circuit but does not directly determine the fundamental principle of charge storage in the capacitor itself.