A dielectric is an insulating material that increases the storage capacity of a capacitor by reducing the electric field within it. Dielectrics are characterized by their ability to be polarized in the presence of an electric field.
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Dielectrics increase a capacitor's capacitance by a factor called the dielectric constant, $\kappa$.
The dielectric constant $\kappa$ is always greater than 1 for any material used as a dielectric.
When inserted between the plates of a capacitor, a dielectric reduces the effective electric field, which allows more charge to be stored at the same voltage.
The energy stored in a capacitor with a dielectric is given by $U = \frac{1}{2} C V^2$, where $C$ is the capacitance and $V$ is the voltage across the capacitor.
Common materials used as dielectrics include glass, ceramic, plastic, and even air.
Review Questions
What effect does inserting a dielectric have on the capacitance of a capacitor?
How does the dielectric constant ($\kappa$) affect the storage capacity of a capacitor?
Why does adding a dielectric reduce the effective electric field within a capacitor?