Resistors use either a series of painted bands or written labels to specify resistance values. Other things that may be on the label include tolerances (the percentage uncertainty between the labeled resistance and the actual resistance), a temperature coefficient rating (not common), and a reliability level rating (reliability that the resistor will maintain its tolerance over a 1000 hour cycle). here are some common labeling schemes used today :

Variable resistors provide varying degrees of resistance that can be set with the turn of a knob. Special kinds of variable resistors include potensiometers, rheostats, and trimmers. Potensiometers and rheostats are essentially the same thing, but rheostats are used specially for high power AC electricity, whereas potensiometers typically are used with lower level DC electricity.

1. CARBON FILM
The most popular resistor type. This resistor made by depositing a carbon film onto a small ceramic cylinder. A small spiral groove cut into the film controls the amount of carbon between the leads, hence setting the resistance. Such resistors show excellent reliability, excellent solderability, noise stability, moisture stability, and heat stability. Typical power ratings range from 1/4 to 2 W. Resistances range from about 10 Ohm to 1 MOhm, with tolerances around 5 percent.

An electrical signal can be amplified by using a device that allows a small current or voltage to control the flow of a much larger current. Transistors are the basic devices providing control of this kind. Modern transistors are divided into two main categories: bipolar junction transistors (BJTs) and field effect transistors (FETs). Applying current in BJTs and voltage in FETs between the input and common terminals increases the conductivity between the common and output terminals, thereby controlling current flow between them. The characteristics of a transistor depend on its type.

The term "transistor" originally referred to the point contact type, which saw very limited commercial application, being replaced by the much more practical bipolar junction types in the early 1950s. Today's most widely used schematic symbol, like the term "transistor", originally referred to these long-obsolete devices.[1]

In analog circuits, transistors are used in amplifiers, (direct current amplifiers, audio amplifiers, radio frequency amplifiers), and linear regulated power supplies. Transistors are also used in digital circuits where they function as electronic switches, but rarely as discrete devices, almost always being incorporated in monolithic Integrated Circuits. Digital circuits include logic gates, random access memory (RAM), microprocessors, and digital signal processors (DSPs).

The color of the generated light depends on the nature of the materials from which the LED is built, more specifically the width of the forbidden zone between the valence band and the conduction band. This also led to one with a long wavelength pass a lower voltage than one with a short wavelength, such as red and blue 3.6 V 1.5 V. Because the voltage on a little rise led to a greater power, the color just move to a shorter wavelength, a blue LED at low power will seem more green and a red LED is (briefly) yellow with so many current piece that he goes.