Design a parallel-plate capacitor that is able to store the same amount of energy as in th...

Design a parallel-plate capacitor that is able to store the same amount of energy as in the AA battery mentioned in Example 19.2. Give the area of the plates, the plate separation, and the composition of the dielectric and determine the voltage across the capacitor.

Example 19.2.

Using a Capacitor as a Source of Electric Energy

There are some similarities between a battery and a capacitor. For instance, both can store energy. In a battery, the energy is stored as chemical energy, and in a capacitor, the energy is stored as electric potential energy. In both cases, this energy can be used to produce an electric current. In some applications in which very high currents are needed for a very short time (such as a camera flash), capacitors are preferred over batteries. A typical capacitor used in this way might have a capacitance of 1.0 F and an initial potential difference of 3.0 V between its plates. Compare the energy stored in this capacitor with the energy stored in an AA battery, which is about 7000 J.

RECOGNIZE THE PRINCIPLE

From Chapter 18, we know that the energy stored in a capacitor is given by

(Eq. 18.33). The values of C and AV are given, so we can calculate PEelecc.

SKETCH THE PROBLEM

No sketch is necessary.

RECOGNIZE THE PRINCIPLE AND SOLVE

Inserting the given values of capacitance and potential difference leads to