ELECTRICITY

        ELECTRICITY

    

                                                                     
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire. In addition, electricity encompasses less familiar concepts such as the electromagnetic field and electromagnetic induction.The word is from the New Latin ēlectricus, “amber-like”, coined in the year 1600 from the Greek ήλεκτρον (electron) meaning amber, because electrical effects were produced classically by rubbing amber.In general usage, the word “electricity” adequately refers to a number of physical effects. In a scientific context, however, the term is vague, and these related, but distinct, concepts are better identified by more precise terms:

·         Electric charge: a property of some subatomic particles, which determines their electromagnetic interactions. Electrically charged matter is influenced by, and produces, electromagnetic fields.
·         Electric current: a movement or flow of electrically charged particles, typically measured in amperes.
·         Electric field: an influence produced by an electric charge on other charges in its vicinity.
·         Electric potential: the capacity of an electric field to do work on an electric charge, typically measured in volts.
·         Electromagnetism: a fundamental interaction between the magnetic field and the presence and motion of an electric charge.

CONDUCTORS
In physics and electrical engineering, a conductor is a material which contains movable electric charges. In metallic conductors such as copper or aluminum, the movable charged particles are electrons (see electrical conduction). Positive charges may also be mobile in the form of atoms bound in a crystal lattice which are missing electrons (known as holes), or in the form of mobile ions, such as in the electrolyte of a battery, or as mobile protons in proton conductors employed in fuel cells. In general use, the term “conductor” is interchangeable with “wire.” Insulators are non-conducting materials with few mobile charges and which support only insignificant electric currents. Copper has a high conductivity. Silver is more conductive, but due to cost it is not practical in most cases. However, it is used in specialized equipment, such as satellites, and as a thin plating to mitigate skin effect losses at high frequencies. Because of its ease of connection by soldering or clamping, copper is still the most common choice for most light-gauge wires.
             
Ohm’s law
A basic law regarding flow of currents was discovered by G.S. OHM in 1828,long before the physical mechanism responsible for flow of currents was discovered

 Ohm’s law states that the” current through a conductor between two points is directly proportional to the potential difference across the two points. Introducing the constant of proportionality, the resistance,one arrives at the usual mathematical equation that describes this relationship”.
                                            
I = V/R
                                    where I is the current through the conductor in units of amperes, V is the potential difference measured across the conductor in units of volts, and R is the resistance of the conductor in units of ohms. More specifically, Ohm’s law states that the R in this relation is constant, independent of the current.
               I = V/R       or       V=IR     or    R=V/I