Diodes & Rectifiers = Diodes and Rectifiers are electronic parts that act as one way valves, they can be used to block destructive back flow of power or to turn alternating current  (AC) into direct current (DC). Parts called bridge rectifiers contain four rectifiers hooked together in a square pattern that specifically is made to change AC current into DC more effectively. Bridge rectifiers have four wires, two for the AC and two for the DC output. They are most often housed in a round or square housing.

Resistor = The image at the top is the resistor schematic symbol. The one directly below it is a wire wound square power resistor. The next is the type most often used and it is called a carbon film resistor. The last resistor illustrated is another type of wire wound resistor, wound on a ceramic cylinder. Not part of the illustrated types shown is an obsolete variety called a carbon composition resistor. Carbon composition resistors are found in older equipment. They are not as safe as the carbon film resistors as they can allow arcing when they crack. They are not used in modern circuits for this safety reason. They look like carbon film resistors except the ends are flat instead of round. Resistors are electronic components that are especially made to create a specific level of resistance to the flow of electrons. They are marked with numbers in Ohms or color coded with their Ohms value stated in color bands across the device. They limit the amount of power that a device is exposed to. Note: Watts law must be used to determine the safe wattage for components such as resistors to avoid fire hazards!!!!
 

LED = Led (Light Emitting Diode) are diodes that create radiation in a specific wavelength when a controlled amount of power is sent through them. They can be damaged if overloaded by direct contact with power sources so do not put them across batteries without a resistor unless the voltage characteristics are safe for the unit. The value for the resistors used with a LED must be determined using electronic math.  The radiation LED's create is emitted in the form of light energy particles (photons). Most emit visible light, but some emit I.R. (for night vision, robotics and remote control applications). They will burn and pop if overloaded!!! 

Capacitors = Capacitors store electrical power for later use in a rechargeable material placed in-between two conductive plates. These electrochemical storage devices are similar to batteries except unlike batteries they can take thousands or millions of charge and discharge cycles without failure. They are also different in that they are designed to take a  specific smaller charge instead of a large reserveable charge. They are used in electronics to smooth power fluctuations out, filter signals and to control timing circuits through gradual charging and discharge intervals. They are also used in tuning circuits to provide symbiotic capacitive support to the inductive portions of the circuit. With the exception of non polarized units they must not be put in backwards or they can explode!!!! 

Transistor = Transistors are electronic parts that work like switches, but unlike switches transistors have no moving parts. Transistors are made of  polarized crystalline materials that have three wires attached to them. One is to collect power, one is to release it and one is to sense a signal to turn on the power through the device.  They have an advantage over mechanical switching devices as they can turn on in varying degrees. This allows them to be used as an electrical valve that can let as much power through as you need, or as little. The three wires on a transistor each have an unique use. The wires are referred to as the Emitter, Collector and Base. The  Collector and Emitter route the main power being controlled by the unit and the Base wire acts as the sensor wire to let the part know what you want it to do and to let it turn on a large amount of power with very little power to signal it. The ability of the base being able to switch large amounts of power with a small amount of power allows the transistor to be used as an amplifier.
     Electronic math should always be used to help pick the right transistor for a specific job as overloading an underrated unit can led to overheating and burning of the part. Look at circuit examples in books for further clues as to the appropriate use for transistors. Also remember that transistors have come along way since their beginnings as there are many wondrous varieties that would have been considered impossible a few short years ago. The most stunning of these include parts such as VMOS, DMOS and TMOS power FETS which are such efficient switching transistors that they can be selected to turn on motors and other equipment directly. As with other units watch the power ratings and add heat sinks when necessary. Also note that there are two main types of transistors: PNP and NPN, this refers to the polarity they work with. PNP = Positive, Negative, Positive; and NPN = Negative, Positive, Negative.

Phototransistor

Phototransistor = A phototransistor is a light sensitive transistor.

Piezoelectric Tone Source

Piezoelectric Tone Source = Electronic part that used a polarized crystalline disk that bends when exposed to electricity to create sound by rapid vibrating movements.  Danger: Never put a piezo device next to your ear, they can create high dB (sound pressure) sound that can harm hearing at close proximity!!!! They are the same device used in fire alarms and other warning equipment.

PM Field Motors

PM Field Motors = P M field motors are permanent magnet motors that use the electricity provided to them to induce magnetism in their coils, which  turns them across the permanent magnets, thereby rotating the shaft.  A part called a commutator allows the coils to take turns tuning on and off as they go in and out of phase with the permanent magnets. The electricity is conducted to the commutator by metal or carbon brushes that press against the commutator as it rotates.