Physics
Study Material

# Electrostatic Force

The electrostatic force is defined as the attractive or repulsive force between relatively static charged particles. It is referred as Coulomb's force when acting between point charges.

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Posted by Mahak Jain, 8/12/2021 Hesap Oluştur

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The fundamental forces of nature are an attraction or repulsion between objects. There are four fundamental forces in the nature, firstly gravitational force, secondly electrostatic force. Strong and weak nuclear force follows previous forces.

• Gravitational force is in between any two objects that having mass or energy. It is weakest among all the fundamental forces. Gravitational force is always attractive.
• Electromagnetic force Electromagnetic forces are forces created by both electric and magnetic fields for a particle moving with velocity. It is stronger than gravitational force and having infinite range.
• Strong nuclear force is the strongest among all the fundamental forces but short range. It binds protons with charges to the nucleus. It is most attractive in nature but can be repulsive sometimes.
• Weak nuclear force exists between elementary particles. eg this force is responsible for radioactive decay.

Electrostatics deals with the properties of stationary or slow-moving electric charges. Electrostatic phenomena arise from the forces that electric charges exert on each other. Electrostatic forces refer to forces between electric charges which are not moving relative to each other (static) for E being the electric field.

## What is electrostatic force?

Electrostatic force is an attractive or repulsive force between particles having electric charges.

Same charges repel each other,

Opposite charges attracts each other,

Conventionally, the electric force between the two static charged particles is electrostatic force.

## Define electrostatic force

The electrostatic force is defined as the attractive or repulsive force between relatively static charged particles. It is referred as Coulomb’s force when acting between point charges.

Example : the force between the protons and electrons in an atom is electrostatic force. It provides stability of atoms.

Applications of Electrostatic Force :

• Photocopying machines
• As smoke precipitator
• Laser printer
• ink-jet printers
• Smoke precipitator etc.

## Example of electrostatic force

suppose if we rub two glass rods with wool or silk cloth are brought close to each other, they will repel each other.

This is because while rubbing electrons are exchanged between both the objects.The glass rod donate electrons and become positive while silk thread gain electrons become negatively charged. Both the positively charged rod repel each other and silk and glass rod attract each other. This repulsive and attractive force is electrostatic force.

Some other examples of electrostatic forces are,

• The attraction of paper to a charged scale by rubbing to hair.
• The force of attraction of the plastic wrap to one’s hand and later when the hand is removed from the wrap.

## Coulomb’s law and explanation

Coulomb’s law states that “the electrical force between two charged particles is directly proportional to the product of the magnitude of both the charges and inversely proportional to square of distance separating them and acts on line joining both of the charges “.

If two charges q1 and q2 separated by distance r in a vacuum then force between then will be,

F = k q1q2/r2

Here k = Coulomb’s constant. The value of k is 9 × 109 Nm2/C2

Thus, the increasing magnitude of any of the charges, the forces will increase proportionally.

On increasing distance separating both the charges, force will decrease.

## Coulomb’s law derivation

Suppose two charges q1 and q2 separated by distance r,

Now according to coulomb’s law,

Force is directly proportional to product of magnitude of charges,

F ∝ q1 × q2 ………..eq.l

Force is inversely proportional to square of separation distance,

F ∝ 1/r²…………eq.ll

Now by equation l and ll ,

F ∝ q1×q2 / r²

Thus, F = k q1×q2 / r²

Here constant k =1/4πε ( ε is the electric permittivity of the medium)

## Coulomb’s law in vector form

Force is a vector quantity. So vector form of coulomb’s law is,

Assume the position vectors of charges q1 and q2 are r1 and r2 respectively.

The vector leading from 1 to 2 is r21,

r21 = r2 – r1

The vector leading from 2 to 1 is r12

r12 = r1 – r2 = – r21

Now Coulomb’s force law between two point charges q1 and q2 located at

r1 and r2, respectively is expressed as,

F21 : force on q2 due to q1

F12 : force on q1 due to q2

## Difference between electrostatic force and gravitational force

• Electrostatic forces are much stronger than gravitational forces. Gravitational force is the weakest force among all the fundamental forces.
• Electrostatic forces can be either attractive or repulsive in nature, whereas gravitational forces are always attractive in nature.
• Electrostatic forces depend on the medium, whereas gravitational forces do not depend on the medium.