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Dielectrics
Intermediate
Insulators that increase capacitance.
C = κC₀An insulator between plates increases capacitance by factor κ (dielectric constant) and reduces the field by κ. It also raises the breakdown voltage.
Paper κ ≈ 3.7; water 80.
At constant charge voltage drops; at constant voltage charge increases.
In more detail
A dielectric is an insulating material placed between capacitor plates. It increases capacitance by a factor κ, the dielectric constant, by reducing the field for a given charge.
Real-world uses
- Capacitors use ceramic or plastic dielectrics to store more charge.
- Cables use dielectrics to insulate conductors.
- Manufacturers use dielectric materials between capacitor plates to store more charge in a small size.
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Frequently asked questions
Why does a dielectric increase capacitance?
Its molecules polarise and partly cancel the applied field, allowing more charge on the plates.
Is there a limit?
Yes, too high a field causes dielectric breakdown.
What does the dielectric constant do?
It multiplies the capacitance, because the material reduces the field between the plates for the same charge.
Related topics in Electrostatics
Capacitors in parallel · Energy in a capacitor · Energy density of field · Polarisation · Dielectric breakdown · Spherical capacitor