ELECTRICITY , Class X, Part-1

                                                                                                              ELECTRICITY 

     Introduction

Electricity is an important source of energy in the modern times electricity is used in our homes, in industry and in transport. For example, electricity is used in our homes for lighting, operating fans and heating purposes. In industry electrics is used to run various types of machines and in transport sector electricity is being used to pull electric trains. In order to understand electricity we should first know something about electric charges. The flow of electric charges is called “electricity”. Electric charge of two type positive and negative charge.

   Types of electric charges

Electric charges of two type positive and negative charges. The charge acquired by glass rod when rubbed with a silk cloth is called positive charge. The charge acquired by an ebonite rod when rubbed with a woollen cloth is called negative charge.

                        An important property of electric charges

Opposite charges or unlike charges attract each other for example, a positive charges attracts. Similar charges or like charges repeal each other. This is also the fundamental law of electricity. For example, a positive repeal a positive charge and a negative charge repel a negative charge.

                      The S.1 unit of electric charge is coulomb.
Which is denoted by the letter C. One coulomb is that quantity of electric charge which exerts a force of 9x109 newtons on an equal charge placed at a distance of 1 meter from it.                   
Matter contains positively charged particles Called protons and negatively charges particles called electrons. A proton possesses a positive charge of 1.6 x 10-19C. Whereas an electron possess a negative charge of  1.6x10-19 C.
It is obvious that unit of electric charge coulomb is much bigger than the charge of a proton or an electron.
                          CONDUCTORS AND INSULATORS
All the substances can be divided mainly into two electrical categories, conductors and insulators.
Conductors
Those substances through which electric charges can flow are called conductors or Those substances through which electricity can flow easily are called conductors.
Example:- all metals like silver, copper and aluminium etc. The metal alloys such as nichrome , Maganin and constantan .
Metal alloys are also used in making heating elements of electrical appliances such as nichrome, maganin and constantan. In alloys electrical conductivity is much less than that of pure metals.
Carbon in the form of graphite is also a conductor. The human body plant (green) and animal body is a fairly good conductor.
Insulators

Those substances through which electric charges can’t flow are called insulators (Or) those substances through which electricity can’t flow are called insulators.Example glass, ebonite, rubber, plastic, paper, dry air, dry wood, cotton, mica, backelite, porcelain and dry leather are all insulators because they do not allow electric charges (electricity) to flow through them. All the conductors (like metals) have some electrons which are loosely held by the nuclei of their atoms. These electrons are called “free electrons” and can move from one atom to other atoms. Throughout the conductors.The free electrons or presence of free electrons in a substance make it a conductors (electricity).Electricity can be classified into two parts
1.    Static electricity
2.    Current electricity
The electrons present in insulators are strongly held by the nuclei of their atoms, since there are no free electrons in an insulator which can move from one atom to another, an insulator does not allow electric charges (electricity) to flow through it.


 Electric potential (v)

When a small positive text charge is placed in the electric field due to another charge, it experience a force. So work has to be done on the positive text charge to more it against this force of repulsion.

The electric potential (or potential) at a point in an electric field is defined as the work done in moving a unit positive charge from infinity to that point.
 Potential is denoted by the symbol V and its unit is volt. A potential of 1 Volt at a point means that 1 joule of work is done in moving 1 unit positive charge or 1 coulomb of charge from infinity to that point.

 Potential difference (P.D or V)

 The difference in electric potential between two points is known as potential difference.

The potential difference between two point  an electric circuit is defined as the amount of work done in moving a unit charge form one point to the other point.

Where,W = work done     
 Q = quantity of charge moved
The S.1 unit of potential difference  (P.D.) is volt (V).
 



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