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Voltage : Voltage is something is a type of "pressure" that drives electrical charges through a circuit.

Bodies with
opposite charges attract, they exert a force on each other pulling them together. The magnitude of the force is proportional to the product of the charge on each mass. This is just like gravity, where we use the term "mass" to represent the quality of bodies that results in the attractive force that pulls them together.

Electrical force, like gravity, also depends inversely on the distance squared between the two bodies; short separation means big forces.

Thus it takes an opposing force to keep two charges of opposite sign apart, just like it takes force to keep an apple from falling to earth. It also takes
work and the expenditure of energy to pull positive and negative charges apart, just like it takes work to raise a big mass against gravity, or to stretch a spring. This stored or potential energy can be recovered and put to work to do some useful task.

A falling mass can raise a bucket of water; a retracting spring can pull a door shut or run a clock. It requires some imagination to devise ways one might hook on to charges of opposite sign to get some useful work done, but it should be possible.


Electric Charge
Fig - 1 : Opposite charges exert an attractive force on each other

The potential that separated opposite charges have for doing work if they are released to fly together is called voltage, measured in units of volts (V). The greater the amount of charge and the greater the physical separation, the greater the voltage or stored energy. The greater the voltage, the greater the force that is driving the charges together.

Voltage is always measured between two points, in this case, the positive and negative charges. If you want to compare the voltage of several charged bodies, the relative force driving the various charges, it makes sense to keep one point constant for the measurements. Traditionally, that common point is called "ground."

So how do you tell if a particular bunch of charge is positive or negative? You can't in isolation. Even with two charges, you can only tell if they are the same (they repel) or opposite (they attract). The names are relative; someone has to define which one is "positive."

 
Similarly, the voltage between two points A and B , VAB , is relative. If VAB is positive you know the two points are oppositely charged, but you cannot tell if point A has positive charge and point B negative, or visa versa.

However, if you make a second measurement between A and another point C , you can at least tell if B and C have the same charge by the relative sign of the two voltages, VAB and VAC to your common point A . You can even determine the voltage between B and C without measuring it: VBC = VAC - VAB . This is the advantage of defining a common point, like A , as ground and making all voltage measurements with respect to it. If one further defines the charge at point A to be negative charge, then a positive VAB means point B is positively charged, by definition. The names and the signs are all relative, and sometimes confusing if one forgets what the reference or ground point is.

Electric Charge
Fig - 2: Like charges exert a repulsive force on each other.

Learn More on Basics of Electronics:

Electronics Definitions: Electronics is the branch of science that deals with the study of flow and control of electrons (electricity) and the study of their behavior and effects in vacuums, gases, and semiconductors, and with devices using such electrons.

Rules of Electrical Circuits: * A voltage of 1V across a resistance of 1 Ohm will cause a current flow of 1 Amp, and the resistor will dissipate 1 Watt (all as heat).

What is an electronic circuit? A circuit is a structure that directs and controls electric currents, presumably to perform some useful function. The very name "circuit" implies that the structure is closed, something like a loop.

Current: Charge is mobile and can flow freely in certain materials, called conductors. Metals and a few other elements and compounds are conductors. Materials that charge cannot flow through are called insulators. Air, glass, most plastics, and rubber are insulators, for example. And then there are some materials called semiconductors, that seemed to be good conductors sometimes but much less so other times. Silicon and germanium are two such materials. The flow of charge is called electrical current. Current is measured in amperes (a), amps for short (named after another French scientist who worked mostly with magnetic effects).

Wiring Symbols: There are many different representations for basic wiring symbols, and these are the most common.  The conventions I use for wires crossing and joining are marked with a star (*) - the others are a small sample of those in common use, but are fairly representative.  Many can be worked out from their position in the circuit diagram (schematic).

What is charge?  Charge may be defined as the quantity of unbalanced electricity in a body (either positive or negative) and construed as an excess or deficiency of electrons. Charge comes in two forms, positive (+) , and  negative charge ( - ) .

Batteries: Charges can be separated by several means to produce a voltage. A battery uses a chemical reaction to produce energy and separate opposite sign charges onto its two terminals. As the charge is drawn off by an external circuit, doing work and finally returning to the opposite terminal, more chemicals in the battery react to restore the charge difference and the voltage. The particular type of chemical reaction used determines the voltage of the battery, but for most commercial batteries the voltage is about 1.5 V per chemical section or cell.

Resistors: A Resistor is an electrical device that resists the flow of electrical current. It is a passive device used to control, or impede the flow of, electric current in an electric circuit by providing resistance, thereby developing a drop in voltage across the device. The value of a resistor is measured in ohms and represented by the Greek letter capital omega. Resistors usually have a brown cylindrical body with a wire lead on each end, and colored bands that indicate the value of the resistor.

Ohm’s Law: Ohm's law describes the relationship between voltage, V , which is trying to force charge to flow, resistance, R , which is resisting that flow, and the actual resulting current I .

Power: Power is the Electric energy produced per unit time.

Capacitors: In simple words, we can say that a capacitor is a device used to store and release electricity, usually as the result of a chemical action. Also referred to as a storage cell, a secondary cell, a condenser or an accumulator. A Leyden Jar was an early example of a capacitor.

Inductors: An inductor is an electrical device (typically a conducting coil) that introduces inductance into a circuit. An inductor is a passive electrical component designed to provide inductance in a circuit. It is basically a coil of wire wrapped around an iron core. simplest form an inductor is made up of a coil of wire. The inductance measured in henrys, is proportional to the number of turns of wire, the wire loop diameter and the material or core the wire is wound around.

Semiconductor devices: A conductor made with semiconducting material. Semiconductors are made up of a substance with electrical properties intermediate between a good conductor and a good insulator. A semiconductor device conducts electricity poorly at room temperature, but has increasing conductivity at higher temperatures. Metalloids are usually good semiconductors.

Silicon: Silicon, atomic number 14 on the periodic table, is a semiconducting material from which integrated circuits (computer chips of all types--processors, memory chips, etc.; CCDs; transistors; etc.) are created.

Silicon is one of the most common elements. Silicon is also the semiconductor material out of which almost all modern transistors are made.

Diodes: A Diode is an electronic device that allows current to flow in one direction only. It is a semiconductor that consists of a p-n junction. They are used most commonly to convert AC to DC, because they pass the positive part of the wave, and block the negative part of the AC signal, or, if they are reversed, they pass only the negative part and not the positive part.

Electronic Component name abbreviations: Here is a list of Electronic Component name abbreviations widely used in the electronics industry.

Current | Electric Current | AC (Alternate Current) | DC (Direct Current)

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