CBSE Electricity Subject Notes
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 ....
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.
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.
The presence of “free electrons” in a substance makes it a conductor.
Electricity can be classified into two parts:
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
The s.i. unit of potential difference is volt.
Thus 1 Volt = 1 joule/ 1 coulomb
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