Parallel-plate capacitor

Definition

A parallel-plate capacitor is a device that stores electrical energy by maintaining an electric field between two conducting plates separated by an insulating material. The capacitance of the capacitor is determined by the area of the plates, the distance between them, and the dielectric constant of the insulator.

5 Must Know Facts For Your Next Test

1. The capacitance $C$ of a parallel-plate capacitor is given by $C = \varepsilon_0\varepsilon_r \frac{A}{d}$, where $\varepsilon_0$ is the permittivity of free space, $\varepsilon_r$ is the relative permittivity (dielectric constant) of the insulating material, $A$ is the area of one plate, and $d$ is the separation between the plates.
2. Increasing the plate area or decreasing the distance between plates increases the capacitance.
3. The energy stored in a charged parallel-plate capacitor is given by $U = \frac{1}{2}CV^2$, where $V$ is the voltage across the plates.
4. The presence of a dielectric material between plates increases capacitance and reduces electric field strength for a given charge.
5. If a dielectric slab partially fills the space between capacitor plates, it creates regions with different capacitances.

Review Questions

• What happens to the capacitance if you double the plate area while keeping all other factors constant?
• How does inserting a dielectric material between capacitor plates affect its overall capacitance?
• Derive and explain how to calculate stored energy in a parallel-plate capacitor with given voltage and capacitance.

Related terms

Capacitance: The ability of a system to store an electric charge. It is measured in Farads (F).

Dielectric: An insulating material placed between conducting plates that increases their capacitance by reducing electric field strength.

Electric Field: \text{A region around a charged particle or object within which an electric force would be exerted on other charges.}