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 CBSE Electricity Subject Notes CBSE Guess > eBooks > Class X > Electricity by Mr Sanjeev Electricity Chapter - 3 Electricity is an important source of energy in the modern time. It is used in our homes, factories and in transport. For example, it is used in our homes for lighting operating fans and heating purposes. In industries it used for running  many machines and in transport it is used to pull electric trains. It has been founded by the experiments there are two types of charges positive charge and negative charge. By convention, the charge acquired by the glass rod is called positive charge and charge acquired by an abonite rod is called negative charge. An important property of electric charge is following .... Opposite charges attract each other. For example, a positive charge attracts negative charge. Similar charges repel each other. For example a positive charge repel each other. For example a positive charge repel the another positive or negative charge repel the another negative charge. The s.i. unit of electric charge is coulomb which is denoted by the letter C. One coulomb can be define as follow : one coulomb is that quantity of electric charge which exert the force of 9 x 10 9 N on an equal charge placed at  a distance of 1 m from it. We will now know that all the matter containing the positive charge called protons and having negative charge called electrons. a proton possesses a positive charge of 1.6 x 10 -19 C whereas the electron have a negative charge of 1.6 x 10 -19 C.     Note: the s.i. unit of electric charge ‘coulomb’ is equivalent to the charge contained in 6.25 x 10 18 electrons.   Conductors:   those substances through which electricity can flow are called conductors. All the metals like silver, copper, aluminium etc are conductors.. . the metal alloys such as nichrome, manganin and constantan are also conductor of electricity but their conductivity is much less than that of pure metals. Carbon in the form of graphite is also good conductor of electricity and the human body is also good conductor.      Insulators: those substance in which the electric current cannot flow are called insulators. Glass, ebonite rubber, most plastics, paper, dry wood, wood, cotton, mica, Bakelite, and dry air are all insulators because they do not allow electric charges to flow through them. In the case of charged insulator like glass, ebonite etc.. the electric charges remain bound to them, and do not move away. We have just seen that some of the substance are conductors  whereas others are insulators. All the conductors have electrons which are loosely held by the nuclei of their atoms. These electrons are known as , ‘free electrons’. And can move from one place to another throughout the conductors. The presence of “free electrons” in a substance makes it a conductor.   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 place to another, an insulator does not allow electric charges to flow through it. Electricity can be classified into two parts: Static electricity: the electric charge in it do not move. Means remains as rest. Current electricity: the electric charge in it move from one place to another. Electric potential: the electric potential at a point in an electric field is defined as the work done in moving unit positive charge form infinity to that point. It is denoted by volt (V).   One volt: a potential of 1 volt at a point means that 1 joule of work is done in moving 1 unit of electric charge from infinite to that point. Potential difference: the potential difference b/w two points in an electric current is defined as the amount of work in moving a unit charge from one point to other point.                   Potential difference = work done / quantity of charge moved If w joules of work has to be done move Q coulombs of charge form one point to other point, then the potential difference V b/w the points is given by the formula                                                 V = W/Q     where                                            W = work done and Q = quantity of charge The s.i. unit of potential difference is volt. The potential difference b/w two points is said to be 1  volt if one joule of work is done in moving 1 coulomb of electric charge from one to the other. Thus               1 Volt = 1 joule/ 1 coulomb                               1V = 1 /C     Note: the potential difference is measured by means of an instrument having has a high resistance called voltmeter and it always connected in parallel across the points where the potential difference is measured. Electric current: it is the flow of electric charges (electrons) in a conductor such as wire is called electric current. the magnitude of electric current in a conductor is the amount of electric charge passing through a given point of the conductor in one second. If a charge of Q coulomb flow through the conductor in t seconds, then the magnitude of I of the electric current  flowing through it is following                                    Current ( I )= Q /t The s.i. unit of current is ampere which is denoted by the letter ‘ A’.