basic electrical engineering

Basics of electrical engineering

                               knowing the basics of electrical engineering plays an important role in developing strong grip on the electrical engineering practical applications as well as its related subjects.Even strong fundamentals in electrical engineering helps to excel in other streams of engineering 

                                As electricity is the basic source of energy in the present days and electrical engineering got its own importance as electricity can be easily converted to other forms of energy

Basic electrical terms


                                There are two types of charge: positive charge (proton) and negative charge (electron).we neither create nor destroy electrons (or protons).these charged particles exert attraction force on opposite charge and repulsive force on same type of charges.

The S.I unit of charge is coulomb (C).

a single electron has a charge of  −1.602 × 10−19 C and 

a single proton has a charge of    +1.602 × 10−19 C.

Electric Current

                          The continuous flow of electrons constitutes an electric  current.The unit of current is amperes and is denoted by 'I',Current is measured by using ammeter.We define the current at a specific point and flowing in a specified direction as the instantaneous rate at which net positive charge (Q) is moving past  that point in the specified direction.



The material which allows the flow of electrons is called conductor

  • insulator

The material which does not allow the flow of electric current are called insulators

  • voltage

               The voltage across a terminal pair is a measure of the work required to  move charge through the element. voltage  can exist between a pair of electrical terminals whether a current is flowing or not.Voltage is denoted by V.

The voltage difference between any two points is the potential difference


            It is the property of conductor to oppose the flow of  current through it.resistance is denoted by R
units of resistance are ohms
p=specific resistivity
A=area of cross section


            If one joule of energy is expended in transferring one coulomb of charge through the device in one second, then the rate of energy transfer is one watt. The absorbed power must be proportional both to the number of coulombs transferred per second (current) and to the energy needed to transfer one coulomb through the element (voltage). Thus,
                                                         P = VI 
 The units of power is watts

Relation between power,voltage,current,resistance

power loss


                                    Ohm’s law states that the current across conducting materials is directly proportional to the voltage flowing through the material
 Material that obeys Ohm's Law is called "ohmic" or "linear"  because the potential difference across it varies linearly with the current.and which does not obey ohms law are called non ohmic or non linear conductors

Coulomb's law>

                                       The magnitude of the electrostatic force of attraction or repulsion between two  charges is directly proportional to the scalar multiplication of the magnitudes of charges and inversely proportional to the square of the distance between them.
The force acts  along the line joining them.
Coulomb's law and in vector form it is represented as
Coulomb's law 

kirchoff's voltage law(KVL)

                            It states that in a closed circuit the total voltage is zero,i.e the total voltage supplied is equal to the voltage drop in the closed circuit.It is based on law of conservation of energy

kirchoff's current law(KCL)

                    It states that the total current entering a node is equal to the total current leaving the node
in a circuit

Basic elements used in electrical engineering


                                        Resistor provides resistance to the path of current.It is denoted by R the voltage drop across resistor is given by V=IR



It stores energy in the form of magnetic field.voltage across inductor is given by 
voltage in inductor
 from this equation we can say that the “self-induced emf = inductance x rate of current change” and a circuit has an inductance of one Henry will have an emf of one volt induced in the circuit when the current flowing through the circuit changes at a rate of one ampere per second
With a steady state DC current flowing through the inductor and therefore zero induced voltage across it, the inductor acts as a short circuit equal to a piece of wire, or at the very least a very low value resistance. In other words, the opposition to the flow of current offered by an inductor is very different between AC and DC circuits.


    Capacitor is also an energy stori

ng element.Charge (Q) stored in a capacitor is the product of its capacitance (C) and the voltage applied across it(V)
I=C dv/dt
The dv/dt part is derivation of voltage over time, it’s equivalent to saying “how fast is voltage going up or down at this very moment”. If voltage is steady, the derivative is zero, which means current is also zero. This is why current cannot flow through a capacitor holding a steady, DC voltage.

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