This text discusses the physics behind energy conversion processes and a wide variety of energy conversion devices. it first surveys multiple devices that convert to or from electricity including piezoelectric devices, antennas, solar cells, light emitting diodes, lasers, thermoelectric devices, and batteries. This book puts concepts of energy conversion in a more abstract framework and introduce the idea of calculus of variations and illuminate relationships between energy conversion processes.

• ## 3: Pyroelectrics and Electro-Optics

This chapter discusses two additional types of devices that involve material polarization of insulators, pyroelectric devices and electro-optic devices. Pyroelectric devices can convert a temperature difference to a material polarization and therefore electricity, or they can convert a material polarization to a temperature difference. Electro-optic devices can convert optical electromagnetic radiation to a material polarization or vice versa.

• ## 5: Hall Effect

In this chapter we discuss another type of inductive energy conversion device, the Hall effect device. The Hall effect was discovered using gold by Edwin Hall in 1879. The first practical devices were produced in the 1950s and 1960s when uniform semiconductor materials were first manufactured.

• ## 9: Batteries and Fuel Cells

This chapter discusses two related energy conversion devices: batteries and fuel cells. A battery is a device which converts chemical energy to electricity, and one or both of the electrodes of the battery are consumed or deposited in the process. A fuel cell is a device which converts chemical energy to electricity through the oxidation of a fuel. Oxidation is the process of losing an electron while reduction is the process of gaining an electron.

• ## 11: Calculus of Variations

By placing energy conversion processes in a larger framework, we may see relationships between processes or identify additional energy conversion processes to study. Establishing this framework requires some abstraction and hence some mathematics. In the next section, we define the Principle of Least Action and the idea of calculus of variations. In the following sections, we apply these ideas to two example energy conversion systems: a mass spring system and a capacitor inductor system.

• ## 14: Lie Analysis

Lie analysis is a systematic procedure for identifying continuous symmetries of an equation. If the equation possesses continuous symmetries, we may be able to find related conservation laws. Some equations possess multiple symmetries and conservation laws while other equations do not contain any symmetries or conservation laws. Using this procedure with a known generalized path, we may be able to derive conserved quantities even if we do not know how to choose the generalized potential at first