Capacitance

This lecture is based on Serway, Sections 26.1-26.5.

Capacitance is a measure of the ability to store charge given some potential difference. It is defined as
```
            Capacitance = charge / voltage
```
The unit of capacitance is the farad = (coulomb/volt)
A capacitor can store charge, or energy, for later use. It may also be used to filter out transient surges of current in a circuit
To calculate the capacitance of a device, just determine the charge on the device, and the voltage across it.
The equivalent capacitance of two capacitors in parallel is
```
               C(eq)  =  C1 + C2
```

The equivalent capacitance of two capacitors in series is

                 1        1     1
               -----  =  --- + ---
               C(eq)     C1     C2

The energy stored in a capacitor may be expressed as

              E = Q^2/2C  = 0.5*Q*V = 0.5*C*V^2

One may also consider the energy as a function of electric field strength within the volume of the capacitor
```
              E = 0.5*epsilon*E^2
```

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