Diode

Diodes

A diode, or "rectifier,"  is any device through which electricity can flow in only one direction. The first diodes were crystals used as rectifiers in home radio kits. A weak radio signal was fed into the crystal through a very fine wire called a cat's whisker.  The crystal removed the high frequency radio carrier signal, allowing the part of the signal with the audio information to come through loud and clear. The crystal was filled with impurities, making some sections more resistant to electrical flow than others. Using the radio required positioning the cat's whiskers over the right kind of impurity to get electricity to flow through the crystal to the output below it.

At the time, though, no one really understood about the impurities -- then in 1939 Russell Ohl accidentally discovered that it was the boundary between sections of different purity that made the crystal work. Now that the way they work is understood, manufacturers make crystal diodes that work much more consistently than the ones in those original radio kits.

A crystal diode is made of two different types of semiconductors right next to each other. One side is easy for electrons to travel through; one side is much tougher. It's something like trying to swim through a pool filled with water and then a pool filled with mud: swimming through water is easy; swimming through mud is next to impossible. To an electron some semiconductors seem like water, some like mud.  (For more information, read about semiconductors in Everything You Ever Wanted to Know about Conduction.) 

One side of the semiconductor boundary is like mud, one like water. If you try to get electricity to move from the mud side to the water side, there's no problem. The electrons just jump across the boundary, forming a current. But try to make electricity go the other way and nothing will happen. Electrons that didn't have to work hard to travel around the water side just don't have enough energy to make it into the mud side. (In real life, there are always a few electrons that can trickle in the wrong direction, but not enough to make a big difference.) 

This boundary has turned out to be crucial for our daily lives. Diodes change the alternating current that comes from your wall outlet into the direct current that most appliances need. And transistors need two such boundaries to work.

                                                                 INDUCTOR

An inductor is a passive electrical component that produces a voltage proportional to the instantaneous change in current flowing through it:

V = L × dI/dt,

where V is the voltage generated, dI/dt is the rate of change of current, and L is a property of the device called inductance. The SI unit of inductance is the henry(H).

Thus an inductor resists changes in current. A pure inductor does not offer any resistance to direct current (an actual one does slightly), except when the current is switched on and off, then it makes the change more gradual.

When a sinusoidal alternating current flows through an inductor, a sinusoidal alternating voltage (or electromotive force, abbr. emf) is induced. The amplitude of the emf is related to the amplitude of the current and to the frequency of the sinusoid by the following equation.

V = I × ωL

where ω is the angular frequency of the sinusoid defined in terms of the frequency f as

ω = 2πf

The term ωL is known as inductive reactance, which is denoted by the symbol X_L and is the positive imaginary component of impedance.

Construction

An inductor is usually constructed as a coil of conducting material, usually copper wire. A core of ferrous material is sometimes used.

This effect can be understood as follows: the current produces a magnetic field; a change in current gives a change of this magnetic field; a changing magnetic field causes an electromotive force in the conductor. An induction coil is closely related to electromagnets in structure, but used for a different purpose—to store energy in a magnetic field.

Smaller inductors used for very high frequencies are sometimes made with a wire passing through a ferrite cylinder or bead.

History

In 1885, William Stanley, Jr built the first practical induction coil based on Lucien Gaulard and Josiah Willard Gibbs' idea. It was the precursor of the modern transformer.

Synonyms

coil, induction coil, choke, reactor

Resistors

Resistor Color Code Calculator

This resisitor calculator requires the use of Javascript enabled and capable browsers. For operational and other information, and for those unable to use the calculator because of browser limitations, there is a resistor color code chart below the calculator and additional information below the table. For those in the electronics business that are color blind (as I am), working with resistorsand color coded capacitors can be difficult. This table names (as well as shows) the colors and the values. To use the calculator, select a value from the vertical group of Color Band 1, from Color Band 2 and from Color Band 3. Immediately to the left of the Calculate Values button below the three bands, there are three boxes that upon selection of a color from the bands, an identifying number and color will correspond in appearance. After selecting a value from all three bands, click on Calculate Values and the resistor's value is calculated and will appear as well as a text representation of the three bands. This calculator does not consider the 4th Band, tolerance, since it would not change the calculation. You may change a value by again clicking on the band values from any of the three bands but be sure to click on Calculate Values after each selection to update the correct information of resistor value and color band text representation.

Color Band 1 Color Band 2 Color Band 3  OR

Resistor Color Code Chart

Band Color Options Band #1 Possible Band #2 Possible Band #3 Possible Multiplier Value For Band 3 Band #4 Value Tolerance Black 0 1 1 Brown 1 1 1 10 Red 2 2 2 100 Orange 3 3 3 1,000 Yellow 4 4 4 10,000 Green 5 5 5 100,000 Blue 6 6 6 1,000,000 Violet 7 7 10,000,000 Gray 8 8 100,000,000 White 9 9 1,000,000,000 None 20% Silver 10% Gold 5%

Resistor Color Code Information

The resistor color code is a long standing standard in both the electronics and electrical industries, indicating the value of resistance of a resistor. Resistance is measured in ohms and there is a foundation for it called Ohm's Law. (Want to know about Ohm's Law? If so, please click here or click here!) Each color band represents a number and the order of the color band will represent a number value. The first 2 color bands indicate a number. The 3rd color band indicates the multiplier or in other words the number of zeros. The fourth band indicates the tolerance of the resistor +/- 20%, 10% or 5%. In most cases, there are 4 color bands. However, certain precision resistors have 5 bands or have the values written on them, refining the tolerance value even more. There is no standard (TANS) however, for the 5th band. From one manufacturing company to another, the 5th band may indicate 2%, 1%, 1/2% or even closer, according to their own standards. Color bands are usually found on resistors that have a wattage value of 1/8 to 2 watts; though it is rare, there are some 5 watt resistors that are banded. There are also some capacitors that are color coded. See our Capacitor Color Code Calculator.

Capacitors

This article is about the electronic component. For the physical phenomenon, see capacitance. For an overview of various kinds of capacitors, see types of capacitor.

Capacitor
Modern capacitors, by a cm rule
Type	Passive
Invented	Ewald Georg von Kleist (October 1745)
Electronic symbol

A typical electrolytic capacitor

A capacitor (formerly known as condenser) is a device for storing electric charge. The forms of practical capacitors vary widely, but all contain at least two conductors separated by a non-conductor. Capacitors used as parts of electrical systems, for example, consist of metal foils separated by a layer of insulating film.

A capacitor is a passive electronic component consisting of a pair of conductors separated by a dielectric (insulator). When there is a potential difference (voltage) across the conductors, a static electric field develops across the dielectric, causing positive charge to collect on one plate and negative charge on the other plate. Energy is stored in the electrostatic field. An ideal capacitor is characterized by a single constant value,capacitance, measured in farads. This is the ratio of the electric charge on each conductor to the potential difference between them.

Capacitors are widely used in electronic circuits for blocking direct current while allowingalternating current to pass, in filter networks, for smoothing the output of power supplies, in the resonant circuits that tune radios to particular frequencies and for many other purposes.