Class 12 Physics Chapter 1 – Electric Charges and Fields

### Basic Properties of Electric Charge

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#### 1. Additivity of Charges

Additivity of charges means that charges can be add up like real numbers. That is, total charge of the system is simply the algebraic sum of the individual charges. If a system contains n charges q_{1}, q_{2}, q_{3}, … , q_{n}, then the total charge of the system q is just the sum of all individual charges.

That is, charges are scalar quantities like mass. But remember mass of a body is always positive whereas a charge can either positive or negative. So proper sign has to be used while adding the charges in a system.

Example, a system contains charges +2, -3, -5, +4, -1, and +6. So total charge of the system is (+2) + (-3) + (-5) + (+4) + (-1) + (+6) = +3

#### 2. Charge is Conserved

Conservation of charges says that in an isolated system total charge is always conserved. That is, in an isolated system, the charge may get redistribute, but total charge is always remains constant or conserved. It is not possible to create or destroy net charge carried by any isolated system although the charge carrying particles may be created or destroyed in a process.

Example: In frictional electricity, when a glass rod is rubbed with silk, electrons from glass rod moves to silk so that glass rod becomes positively charged and silk becomes negatively charged. But total charge of the system remains same.

#### 3. Quantization of Charge

Quantization of charge states that all free charges are integral multiples of a basic unit of charge denoted by *e*. That is total charge q on a body is

Where n is an integer. The basic unit of charge e is the charge of an electron or proton. Value of e is,

Charge on an electron is taken to be negative; therefore, charge on an electron is written as -e and that on a proton as +e.

Charge of any body can also increase or decrease in steps of e only.