## Conservation of charge Class 12

Just as in mechanics, the total linear momentum of an isolated system always remains constant, and the electric charge also obeys a similar law. It is called the law of conservation of charge.

It states that for an isolated system, the net charge always remains constant. In any physical process, the charge may get transferred from one part of the system to another, but the net charge will always remain the same. In other words, the charge can neither be created nor destroyed.

The following examples explain the law of conservation of charge: 1. We know that when a glass rod is rubbed with silk, the glass rod becomes positively charged and silk becomes negatively charged. The amount of positive charge on the glass rod is found to be exactly the same as the negative charge on silk. Thus, the system of glass rod and silk, which had zero net charge before rubbing, still possesses zero net charges after rubbing.

2. In all nuclear transformations, the proton number is found to remain

unchanged. For example, in the nuclear fission of uranium (92U235) by a neutron (¹), barium (Ba¹41), krypton (Kr92), and three neutrons are produced along with the liberation of energy. The nuclear reaction may be represented as below:

0n1+92U235+-------> 56Ba141+ 36Kr92+30n1+energy

Proton number before fission=0+92=92 Proton number after fission=56+36+3(0)=92
Thus, the net charge (proton number) is the same before and after the nuclear fission of U235

3. Annihilation of matter (a positron and an electron combine to produce a y-ray photon) and pair production (a y-ray photon materializes into an electron and positron pair) are two important nuclear phenomena. Charges are conserved in both two processes.

## Properties of Electric Charge class 12

The following are a few important properties of electric charge :

1. Like charges repel each other and unlike charges attract each other. 2. The magnitude of elementary negative or positive charge is the same and is equal to 1-6 x 10-19 C.

3. The electric charge is additive in nature. It implies that the total charge on an object is the algebraic sum of the charges located at different points in the object.

4. The charge is quantized i.e. charge carried by a charged object is equal to +or- ne, where n is an integer.

5. The electric charge of a system is always conserved. 6. Unlike mass, the electric charge on an object is not affected by the motion of the object.

6. Unlike mass, the electric charge on an object is not affected by the motion of the object.