Capacitors

AP Physics

CapacitorsWhat are they?

A device that stores electrical potential energy by storing charge.

How is that useful?Capacitors are used when a lot of energy is needed quickly (brief burst of power)

What does a capacitor consist of?Any two conducting objects separated by a vacuum or other type of insulating material.

CapacitanceThe ratio of the magnitude of the

charge Q on either conductor to the magnitude of the potential difference V between the conductors.

The Farad is named after the English physicist/chemist Michael Faraday who had many valuable contributions in the field of electromagnetism.

Parallel Plate CapacitorsCapacitor with two parallel plates of

area A and separation distance d.

The electric field between the plates is uniform.

The capacitance of a parallel plate capacitor is:

Notice: Capacitance of a parallel plate capacitor is not dependent on the charge of the capacitor, but rather on the dimensions of the plates and the separation.

Parallel Plate CapacitorA parallel plate capacitor has a capacitance of 1.0 F, and the plates

are 1 mm apart. What is the area of the plates?

This is about 10 km per side…bigger than Manhattan!!Common values for capacitance are microfarads (1 μF = 10-6 F) and picofarads (1 pF = 10-12 F)

Capacitor EnergyThe oppositely charged plates of a capacitor are comparable to

a stretched spring or an object lifted to a higher gravitational potential energy.

The energy stored in a capacitor is: