# PHYS 2212 Module 4 4: Capacitance

The tree-like branch patterns in this clear Plexiglas® block are known as a Lichtenberg figure, named for the German physicist Georg Christof Lichtenberg (1742–1799), who was the first to study these patterns. The “branches” are created by the dielectric breakdown produced by a strong electric field. (credit: modification of work by Bert Hickman)

Capacitors are important components of electrical circuits in many electronic devices, including pacemakers, cell phones, and computers. In this module, we study their properties, and, over the next few chapters, we examine their function in combination with other circuit elements. By themselves, capacitors are often used to store electrical energy and release it when needed; with other circuit components, capacitors often act as part of a filter that allows some electrical signals to pass while blocking others. You can see why capacitors are considered one of the fundamental components of electrical circuits.

Now that we’ve developed a good understanding of electric potential energy, voltage, and their relationships to electric fields, we will apply this knowledge to a device called a capacitor. Capacitors store electric charge and electric potential energy. They are used all over the place, like in electric circuits and also in defibrillators. Here is a short video that shows how a defibrillator works:

#### 4.1 Capacitors and Capacitance

• Explain the concepts of a capacitor and its capacitance
• Describe how to evaluate the capacitance of a system of conductors

#### 4.2 Capacitors in Series and in Parallel

• Explain how to determine the equivalent capacitance of capacitors in series and in parallel combinations
• Compute the potential difference across the plates and the charge on the plates for a capacitor in a network and determine the net capacitance of a network of capacitors

#### 4.3 Energy Stored in a Capacitor

• Explain how energy is stored in a capacitor
• Use energy relations to determine the energy stored in a capacitor network

#### 4.4 Capacitor with a Dielectric

• Describe the effects a dielectric in a capacitor has on capacitance and other properties
• Calculate the capacitance of a capacitor containing a dielectric

#### 4.5 Molecular Model of a Dielectric

• Explain the polarization of a dielectric in a uniform electrical field
• Describe the effect of a polarized dielectric on the electrical field between capacitor plates
• Explain dielectric breakdown