Power electronic deal with how to control and convert power (electric energy) into one form to another and how utilization of power at high efficiency

The field-effect transistor (FET) is a three-terminal device used for a variety of applications that match, to a large extent, those of the BJT transistor. Although there are important differences between the two types of devices, there are also many similarities that will be pointed out in the sections to follow. The primary difference between the two types of transistors is the fact that the BJT transistor is a current-controlled device as depicted in Fig.1a, while the JFET transistor is a voltage-controlled device as shown in Fig.1b.

One of our first concerns in the sinusoidal ac analysis of transistor networks is the magnitude of the input signal. It will determine whether small-signal or large-signal techniques should be applied. There are two models commonly used in the small-signal ac analysis of transistor networks: the re model and the hybrid equivalent model.

Late adulthood - period that begins in the 60s and lasts until death .
§ Late adulthood is the time of:
adjusting to retirement.
decreasing strength and health.
new social roles.
reviewing one’s life. 

The transistor is a three-layer semiconductor device consisting of either two n- and one p-type layers of material or two p- and one n-type layers of material. The former is called an npn transistor, while the latter is called a pnp transistor. In Fig. below both biasing potentials have been applied to a pnp transistor, with the resulting majority- and minority-carrier flow indicated.

The label semiconductor itself provides a hint as to its characteristics. The prefix semi-is normally applied to a range of levels midway between two limits. The term conductor is applied to any material that will support a generous flow of charge when a voltage source of limited magnitude is applied across its terminals. An insulator is a material that offers a very low level of conductivity under pressure from an applied voltage source. A semiconductor, therefore, is a material that has a conductivity level some-where between the extremes of an insulator and a conductor

Early adulthood
 begins in late teens/early 20year and lasts through the 30 year. 
Early adulthood is a time of:
 establishing personal and economic independence
 developing a career