Concept of Current and Voltage

An electric current is formed when electrons flow through a material. In simple language we can say current is like a flow of water in pipe. Assume that the water flowing through a pipe is like current.

Normally copper wire is used for transmission of current .Electrons normally rotate around the nucleus of each atom of copper in the wire, but when electrical pressure (that is the voltage) from a battery or generator is applied, some of these electrons are forced out of their orbits and pass from atom to atom along the length of the wire. These electrons are called free electrons and come from the outer orbit of the atom.

The amount of current depends on the number of electrons passing a given point in a circuit each second. It is measured in Amperes (A) using an apparatus called an Ammeter. An ammeter must be connected in series with other devices in a circuit. The letter I is used to signify the amount of current in a circuit.

Voltage is the potential energy that makes the electrical current flow in a circuit by pushing the electrons around. Voltage is like pressure on water in a pipe flowing from upper side to lower side .voltage means pressure on electrons to flow .The unit of voltage is volt shown as 'v'. And it is measured by voltmeter.

What is a resistor?

A resistor is an electrical element that limits or controls the flow of electrical current in an electronic circuit. Resistors can also be used to afford an exact voltage for an active device such as a transistor.

A resistor has two terminals diagonally which electricity must pass, and is designed to drop the voltage of the current as it run from one terminal to the next. A resistor is primarily used to generate and maintain a known safe current within an electrical component. Unit of resistor is Ohm’s (Ω).

Imagine water flowing through a pipe. If we make the pipe thin then this will restrict the flow of water. If we force the water (current) through the narrow gap by increasing the pressure (voltage) then energy will be given off as heat. In addition, there will be an important difference in pressure (voltage) above and below the restriction.

In electronics we use a resistor when we need to reduce the voltage applied to a circuit.
A resistor is covered with paint or enamel, or covered in molded plastic to protect it. Because resistors are often too small to be written on, a standardized color-coding system is used to identify them.

The first three colors represent ohm value, and a fourth indicates the tolerance, or how close by percentage the resistor is to its ohm value. This is important for two reasons: the nature of resistor structure is imprecise, and if used above its maximum current, the value of the resistor can change or the unit itself can burn up.

Types of materials

Conductors

Conductors are material that easily allow electrical current pass through them with very-less opposition. Almost all metals are conductors. When ever you cut an electric wire, you can see copper or some other metal at its core. It’s because these metals can easily conduct electricity. Silver can conduct electricity better than copper; copper can conduct electricity better than gold. We don't use them because they are tremendously Costly due to their scarcity. In cases where electrical circuit needs to be short, like in PC B's and in IC's, gold has been used. Gold is chosen over silver because it’s static and doesn't retort
And / or corrode as quickly as silver. Examples of conductors are copper, silver, gold, aluminum, steel etc.

Insulators

Insulators are that material that does not conduct electricity under normal conditions. For instance: air is an insulator. You don't get electrocuted when forthcoming a plug point since air is an insulator. In irregular situations, air behaves like a conductor. For example, during a thunderstorm, extremely high voltage creates lightning bolts, which jump from one cloud to another or to the ground. At these excessive conditions, air will act as a conductor. Examples of insulators are plastic, rubber, paper, wood etc. 

Semiconductor

Semiconductors are materials that act like both conductors and insulators. In certain condition a semiconductor acts like a conductor. For example charcoal and graphite which are allotrope of Carbon act as conductor. Whereas diamond which has a different crystal structure act as an insulator. The conductivity of semiconductors can be improved
By adding certain impurities to them this is called doping. The conductivity may improve by pumping energy into semiconductor crystal in the form of heat or light. Example of is silicon, germanium etc.

What is electronics?

Electronics refers to the flow of charge (moving electrons) through nonmetal conductors (mainly semiconductors), whereas electrical refers to the flow of charge through metal conductors. An electronic element is any physical unit in an electronic system whose meaning is to affect the electrons or their related fields in a preferred way

consistent with the proposed function of the electronic system.

Components are generally anticipated to be in mutual electromechanical contact, usually by being soldered to a printed circuit board (PCB), to create an electronic circuit with a particular function (for example an amplifier, radio receiver, or oscillator). Components may be packaged individually or in more complex groups as integrated circuits. Some common electronic components are capacitors, resistors, diodes, transistors, etc.

Electronics is different from electrical and electro-mechanical science and technology, which pact with the generation, distribution, switching, storage and conversion of electrical energy to and from other energy forms using wires, motors, generators, batteries, switches, relays, transformers, resistors and other passive components.

Electric charge is a physical property of substance which causes it to experience a force when near other electrically charged substance. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual disgusting force, as do two negatively charged objects. Positively charged entity

and negatively charged entity experience an attractive force. The SI unit of electric charge is the coulomb (C).

An atom is a particle of substance that individually defines a chemical element. An atom consists of a innermost nucleus that is usually bordered by one or more electrons. Each electron is negatively charged. The nucleus is positively charged, and encloses one or more comparatively important particles known as protons and neutrons.

The total mass of an atom, counting the protons, neutrons and electrons, is the atomic mass or atomic weight. Electrons donate only a tiny part of this mass. For most practical reason, the atomic weight can be thought of as the number of protons plus the number of neutrons. Because the number of neutrons in an atom can vary, there can be several different atomic weights for most elements.

Atoms having the same number of protons, but different numbers of neutrons, characterize the same element, but are known as different isotopes of that element. The isotope for an element is specified by the addition of the number of protons and neutrons.

Protons and electrons have equal and opposite charge, and normally an atom has equal numbers of both. Thus, atoms are frequently neutral. Anion is an atom with extra electrons or with a need of electrons, resulting in its being electrically charged. An ion with extra electrons is negatively charged and is called an anion; an ion lacking in electrons is positively charged and is called a cat ion.