# Capacitance

Start with two parallel plates connected to a battery. A potential is set up between them. If a conductor is placed between them, charge will flow.
If there is no conductor, static charge will be stored. If an insulating material called a dielectric (such as paper or paraffin) is placed between
them, a higher level of charge will be built up.

We call this a parallel plate capacitor.

When two plates are placed in this configuration, there is a proportional relationship between potential difference and total charge. We call this
relationship Capacitance (C). The units for capacitance are Farads (F). **C = Q/V**. Typical capacitors in use in circuits today have
capacitance in the microfarad (10 ^{-6} F) to picofarad ( 10 ^{- 12} F) range.

Recall that **V = Ed**. For two parallel plate capacitors, the electric field is uniform. If **A** is the area of the
plates, **d**is the distance between the plates, and

**e**0is the permittivity of free space, then

**V**

= Qd/

= Qd/

**e**

_{0}**A**and

**C =**

**e**

_{0}**A/d.**

Capacitance is directly proportional to the area of the plates and inversely proportional to the distance between the plates. In a graph of charge vs. potential, the slope of the line represents our capacitance and the area under the curve represents the energy stored.

In a graph of charge vs. potential, the slope of the line represents our capacitance and the area under the curve represents the energy stored.

The energy stored = 1/2 CV^{2}. Units are Joules.

For more information on parallel plate capacitors and capacitance, click on the below links:

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/capac.html#c1

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/pplate.html#c2

For Practice Problems, Try:

*Giancoli Multiple Choice Practice
Questions (Go ahead - try a few.)*