Basic Electrical Concepts

Electricity

Electricity plays an important role in our day to day life. All of us are aware of the various functions that electric city can perform. It is used for lighting , heating , cooling , entertainment , transportation ,calculation many other purposes. In Fact , Now days , All our activities are totally dependent upon electricity. 

The invisible energy which constitutes the flow of electron in an closed  electric circuit to do work is called Electricity.

It is the form of energy which can be converted to any other form very easily. In the past , it was through that electricity is a matter which flow through the circuit to do work.

Electric Potential 
When a body is charged, either electron are supplied to it or the are removed from it. both the case , work is done this work done is stored in the body in form of electric potential. thus , the body has the ability to do work by exerting a force of attraction or repulsion on the other charged particles.

The capacity of a charged body to do work is called electric potential.
Electric Potential = Work Done /charge 
                            V = W/Q

Potential Difference
When a body is charged to a difference electric potential as compared to the other charged body, the two bodies are said to have a potential difference. Both bodies are under stress and strain and try to attain minimum potential,

The difference in the electric potential of the two charged bodies is called potential difference. the unit of potential difference is Volt.

Electric Current
In Metals, large number of free electrons are available which move from one atom to the other at random. When the an electric potential difference is applied across the metallic wire, the loosely attached free electrons start moving towards the positive terminal of the cell. this continuous flow of the electrons constitutes the electric current.

A Continuous flow of electrons in an electric circuit is called electric current.  

R = Resistance

 I = Current

E = e.m.f

Show the fig. metal conductor is connected by battery with resistance. the current start flowing after connecting battery .the current is denoted by I which continuous flow in circuit.   

Resistance   
when a potential difference is applied across the conductor, the free electron start moving in particular direction. While moving through the material, these electrons collide with other atoms and molecules. They oppose this flow electrons (current) through it. This opposition called resistance.

The opposition offered to the flow of current is called resistance    

Heat is produced because of the collisions of moving electrons with other atoms and molecules. The unit of resistance is ohm  and symbol is Ω.

show the fig the battery terminal  is connected across the resistance.   Resistance is denoted by R.

Conductance
The ease to flow of current is called conductance it is generally denoted by letter G. the conductance just reciprocal of resistance the unit of conductance is mho.  the symbol of unit is ℧. show the fig. the conductor in which current flowing the property of conductor the current flows is called conductance.

E.M.F. ( Electromotive Force)
The e.m.f. of source say a battery, is a energy that it gives to each of coulombs of charge. The amount of energy supplied by source to each coulomb of charge is known as e.m.f. of the source.
Shows the fig. A battery has e.m.f suppose 12 V , it means that battery supplies 12 joules of energy to each coulomb of charge travels from + ve terminal to - ve terminal through external circuit, it gives up whole of energy originally supplied by the battery.

Ohm's Law     
When an electric potential difference  (V) is applied across a conductor , some current (I) flows through it the flow of current is opposed by the resistance (R) of the conductor show in fig. A definite relation exists among the three quantities applied voltage , current and resistance. this relation was first given by a German Scientist george Simon Ohm and is called Ohm's law.

Ohm's Law states that the current flowing between any two points of a conductor is directly proportional to the potential difference across them but physical quantity temperature do not change.

So     I ∝ V
         V/I = Constant
This constant called the Resistance (R) of the conductor.
         V/I = R
Also written
         V = IR (Voltage drop)
In the any circuit Current flows through a resistance then potential difference across the resistance known as  drop across it.

Kirchhoff's Laws
  A german scientist Kirchhoffs find two laws known as kirchhoffs law.

First Law: This law relates to the current at the junction points of a circuit and this law called kirchhoffs current law (KCL). KCL states that the algebraic sum of all "the currents meetings at the a point or juction is zero".

Mathematically
                          ∑I = 0

Algebraic sum is to be taken all currents

Applying KCL to juction O,

I1 + I2 − I3 + I4 − I5 − I6 = 0

I1 + I2 + I4 = I3 + I5 + I6

Incoming current = Outgoing current.

The sum of incoming currents is equal to the sum of outgoing currents at a points or junction in any network .

Second law: This law use ti voltage drop and e.m.f in a any circuit and also called voltage  law.It is state that " In any closed circuit or mesh the algebraic sum of all the electromotive forces and the voltage drop is equal to the zero".

Algebraic sum of e.m.fs + Algebraic sum of voltage drop = 0

∑ E + ∑IR = 0

While applying Kirchhoffs second law to a closed circuit, it is very important to assign proper signs to e.m.fs and voltage drop in the closed circuit. The following signs are followed.

A Rise in potential takes positive and fall in potential takes negative.