## Electric charge

Electricity is the factor by which charge is generated in any object or substance. When a substance becomes electrostatic, the substance acquires charge.

Therefore such a substance is called a charged substance.

There are two types of electric charges. Those substances which accept charge have an excess of charge and those substances which give up charge have a deficiency of charge.

**1**. Positively charged

**2**. Negatively charged

Thus,

Electric charge is the basic reason which produces the property of attraction in any object.

An object becoming positively charged reflects the lack of electrons in its atoms.

An object becoming negatively charged indicates an excess of electrons in its atoms.

### Conservation of electric charge

According to this theory,

Electric charge can’t neither be created nor destroyed

**1**. Pair destruction

**2**. Pair production

#### Unit of electric charge

Its unit is coulomb. It is represented by C.

Electric current = electric charge/time

i=q/t

**q=it**

** **

## 1 Coulomb

If a current of 1 ampere flows in a conductor for 1 second, then the amount of charge passing through that conductor will be 1 coulomb.

### Basic charge

If an object has a charge q, then this charge will be an exact multiple of a certain charge (e). This fixed (e) charge is called fundamental charge.

In other words,

q=n.e

This property is called quantization or atomicity of charge.

Thus the value of e will be 1.6×10⁻¹⁹ Coulomb.

## Coulomb’s law

According to Coulomb’s law,

The force of attraction or repulsion between two stationary charges is proportional to the product of the quantities of both the charges and inversely proportional to the square of the distance between them and the direction of the force is along the line joining the charges.

Suppose there are two point charges q₁ and q₂ and the distance between them is r, hence according to Coulomb’s law the force between them is –

F ∝ q₁.q₂_____(1)

F ∝ 1/r²______(2)

F ∝ q₁.q₂/r²

F = K.q₁.q₂/r²

Where K is the constant of proportionality. Its value depends on the distance between charges and the units of force.

**Case 1.**

If both the charges are located in vacuum or air then

K=1/4π€0

K=9×10⁹ N.m²/C²

Where €0 is a constant called the electronegativity of vacuum.

### Numeric value of €0

1/4π€0=9×10⁹

€0=1/4π.9×10⁹

€0=8.85×10⁻¹² C²/N.m²

**Case 2.**

Fm=[1/4π€0].[q₁.q₂/r²]_______(1)

Coulomb force in vacuum

F=K.q₁.q₂/r²________(2)

From equation (1) (2)

F/Fm=K

### Vector form of coulomb’s law

Let the origin be O and two point charges q₁ and q₂ are placed in vacuum at points A and B.

Distance between q₁ and q₂ is r.

Therefore, the electric force acting on q₁ due to charge q₂,

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