As we know that a body can be charged by rubbing it against some other suitable body. If another body is brought it in contact with such a charged body , it also gets charged . It acquires the charge of the sign as that of the charged body . If a positively charged body is brought in contact with an unchanged body , then electrons flow from the unchanged body to it. On the unchanged body, then electrons flow from the unchanged body to it . On the other hand, if a negatively charged body is brought in contact then electrons flow from it to the body to be electrified. Such a process is called the charging of a body by conduction.
However, there is another method by which a body may be charged. If a charged body say a glass rod rubbed with silk is brought near an isolated conductor , it is found that charge of opposite kind is developed on the near end of the conductor and charge of same kind on the far end . However, if the charged body is moved away from the conductor, the charges developed on its two ends disappear.
This temporary electrification of ap conductor, when a charged body is brought near it , is called ELECTROSTATIC INDUCTION.
In contrast to conduction, there is no transfer of electrons between the two bodies during by induction .It is because no physical contact takes place between the charging body and the conductor.
EXPLANATION. When positively charged glass rod is brought near the conductor AB, it attracts the free electrons present in there conductor towards it .As a result, the electrons accumulate at the near end A and therefore, this end becomes negatively charged. As the far end B becomes deficient of electrons it acquires positive charge. The opposite kind of changes appear merely due to the redistribution of electrons in the conductor. This redistribution of electrons takes place instantaneously, when the charged glass rod is brought near the conductor.
The two kinds of charges that appear on the two ends of the conductor due to electro-static induction are called induced charges.
The charge present on the charging body is called inducting charge . It is found that the either kind of the induced charge is equal to the inducting charge. If the charging body is removed, the charges induced on the conductor disappear. Thus , induced charges stay on the conductor only so long as the charging body is kept held near the conductor. ADDITIVE NATURE OF CHARGE:. We know that mass of an object is equal to the sum of the masses of its constituent particles. Owing to this , mass is said to be additive in nature. Like mass, electric charge also possess additive property. The total electric charge of an object is equal to the algebraic sum of all the electric charges distributed on the different parts of the object. If q1 ,q2 , q3 ,………… are electric charges present on different parts of an object then total electric charge on the object, q= q1+q2+q3+………………… It may be pointed out that while taking the algebraic sum, the sign (positive or negative) of the electric charges must be taken into account . The additive property of mass and electric charge differ on following two accounts: 1. The masses of the particles constituting an object are always positive, whereas the charges distributed on the different parts of the object may be positive or negative. 2. The total mass of an object is always non-zero , the total charge on the object may be positive or negative. QUANTIZATION OF CHARGE:. The magnitude of charge on a proton or an electron called elementary charge . Since protons and electrons are the only charged particles constituting the matter , the charge on an object must be integral multiple of +,- e. In other words, the charge possessed by an object can not be a fraction of +,-e. Mathematically, the charge on any object must always be equal to q = (+,-) ne, where N is an integer. Further the charge on an object can be increased or decreased in steps of e. It is because, during process, an integral number of electrons can be transferred from one body to the other body . It is known as QUANTIZATION OF CHARGE OR DISCRETE NATURE OF CHARGE. The discrete nature of electric charge is usually not observable in actual practice . It is because, step size of the electric charge (e) is very small . Due to this number of elementary charges involved becomes extremely large, even when the electric charge on an object is changed by a very small amount .