If Resistors square measure the foremost basic passive element in electrical or electronic circuits, then we've got to think about the Signal Diode as being the foremost basic “Active” element.


However, in contrast to a resistance, a diode doesn't behave linearly with regard to the applied voltage because it has associate degree exponential I-V relationship and thus can't be delineated just by exploitation Ohm’s law as we have a tendency to do for resistors.

Diodes square measure basic unidirectional semiconductor devices which will solely permit current to flow through them in one direction solely, acting additional sort of a method electrical valve, (Forward Biased Condition). But, before we've got a glance at however signal or power diodes work we have a tendency to 1st have to be compelled to perceive the semiconductors basic construction and idea.

Diodes square measure made of one piece of Semiconductor material that includes a positive “P-region” at one finish and a negative “N-region” at the opposite, associate degreed that includes an electrical resistance price somewhere between that of a conductor and a material. however what's a “Semiconductor” material?, first let’s check out what makes one thing either a Conductor or associate degree material.
Resistivity

The electric resistance of associate degree electrical or electronic element or device is mostly outlined as being the magnitude relation of the voltage distinction across it to this flowing through it, basic Ohm´s Law principals. the matter with exploitation resistance as a measuring is that it depends on a great deal on the physical size of the fabric is measured moreover because the material out of that it's created. as an example, if we have a tendency to were to extend the length of the fabric (making it longer) its resistance would conjointly increase proportionately.

Likewise, if we have a tendency to multiplied its diameter or size (making it fatter) its resistance price would decrease. thus we would like to be ready to outline the fabric in such the simplest way on indicating its ability to either conduct or oppose the flow of electrical current through it despite what its size or form happens to be.

The quantity that's accustomed indicates this specific resistance is termed electrical resistance and is given the Greek image of ρ, (Rho). electrical resistance is measured in Ohm-metres, ( Ω-m ). electrical resistance is that the inverse to the physical phenomenon.

If the electrical resistance of assorted materials is compared, they will be classified into 3 main teams, Conductors, Insulators and Semi-conductors as shown below.
Conductors

From higher than we have a tendency to currently understand that Conductors square measure materials that have terribly low values of electrical resistance, typically within the micro-ohms per metre. This low price permits them to simply pass associate degree electrical current as a result of there being lots of free electrons floating regarding among their basic atom structure. however, these electrons can solely flow through a conductor if there's one thing to spur their movement, which one thing is associate degree electrical voltage.

When a positive voltage potential is applied to the fabric these “free negatrons” leave their parent atom associate degreed travel along through the fabric forming an electron drift, additional usually referred to as a current. however “freely” these electrons will move through a conductor depends on however simply they will separate from their constituent atoms once a voltage is applied. Then the quantity of electrons that flow depends on the quantity of electrical resistance the conductor has.

Examples of sensible conductors square measure usually metal like Copper, Aluminium, Silver or non-metals like Carbon as a result of these materials have only a few electrons in their outer “Valence Shell” or ring, leading to them being simply knocked out of the atom’s orbit.

This allows them to flow freely through the fabric till they meet up with alternative atoms, manufacturing a “Domino Effect” through the fabric thereby making associate degree electrical current. Copper and aluminium is that the main conductor utilized in electrical cables as shown.

electrical cable

An cable uses Conductors and Insulators Generally speaking, most metals square measure, sensible conductors of electricity, as they need terribly tiny resistance values, typically within the region of micro-ohms per metre. whereas metals like copper and aluminium square measure superb conducts of electricity, they still have some resistance to the flow of electrons and consequently don't conduct absolutely.

The energy that is lost within the method of passing associate degree electrical current, seems within the style of heat that is why conductors and particularly resistors become hot. conjointly the electrical resistance of conductors will increase with close temperature as a result of metals are usually sensible conductors of warmth.

Insulators

Insulators on the opposite hand square measure the precise opposite of conductors. they're the product of materials, usually non-metals, that have only a few or no “free electrons” floating regarding within their basic atom structure as a result of the electrons within the outer valence shell square measure powerfully attracted by the charged inner nucleus.

In alternative words, the electrons square measure stuck to the parent atom and might not move around freely thus if a possible voltage is applied to the fabric no current can flow as there aren't any “free electrons” offered to manoeuvre and which provides these materials with their insulating properties.

Insulators even have terribly high resistances, scores of ohms per metre, the associate degreed square measure usually not stricken by traditional temperature changes (although at terribly high temperatures wood becomes charcoal and changes from a material to a conductor). samples of sensible insulators square measure marble, amalgamate quartz, p.v.c. plastics, rubber etc.

Insulators play a really necessary role among electrical and electronic circuits, as a result of while not them electrical circuits would short along and not work. as an example, insulators product of glass or ceramic ware square measure used for insulating and supporting overhead transmission cables whereas epoxy-glass rosin materials square measure accustomed create computer circuit boards, PCB’s etc. whereas PVC is employed to insulate electrical cables as shown.