Static Electricity Interview Question Answer

Important Questions of Electrostatics

In this post, some of the important questions of electrostatics are given. It includes definition of static electricity, meaning of molecules and atoms, positive ions and negative ions, glass rubbed with silk, importance of permittivity, absolute permittivity of air, relative permittivity, coulomb first law, coulomb second law, definition of electric field, definition of lines of force, current does not flow in dielectric material, definition of electric field, electric intensity, dielectric strength, potential and factor of safety.

Explain the term: Static – electricity 

Static electricity

When two charges bodies are separated by insulating medium, the charges remain stationary on the body. This is called static electricity.

The branch of engineering which deals with the study of static – electricity is called electro statics.

What do you mean by the molecule and atoms?


The smallest part of the substance is called molecule.


A molecule consists of one or more substance is called as atoms.

When atom becomes positive ion and negative ion?         

Positive ion and Negative ion

If an atom loses an electron, it becomes positive charged. This atom is known as positive ion. Similarly, when atom gain an electron, it becomes negative charged.

Describe the main reason for production of electro static charge when glass is rubbed with silk.       

Electro – static charges

When glass is rubbed with silk, glass loses electrons to silk and therefore it becomes positive charged. Similarly, when ebonite is rubbed with fur, ebonite gains electrons from fur and becomes negative charged.

Describe the importance of permittivity.   

Importance of permittivity

The permittivity affects the magnitude of the force between two-point charges. Higher the value of permittivity placed between two-point charges lesser the force between them and vice versa.

State the value of the absolute permittivity for air.    

Absolute Permittivity

The absolute permittivity of the air ( ε0 ) or vaccum is minimum and its value is limited to 8.854 × 10-12 farad / meter. The value of absolute permittivity of other material is more than ε0.                                                                 

Define: relative permittivity      

Relative permittivity ( εr )

The ratio of the absolute permittivity of some material to the absolute permittivity of the air is called as relative permittivity. Therefore

           εr = ε / ε0


εr  = Relative permittivity of the material

ε  = Absolute permittivity of the material

ε0  = Absolute permittivity of the air ( Farad  / Meter )

State the coulomb’s first and second law. 

Coulomb first law

The first law explains the nature of the force between two charged bodies. It states that’ like charges of electricity repel each other whereas unlike charges attract each other’.

Coulomb second law

The second law explains the magnitude of the force between two charges. It states that ‘The force between two charges is directly proportional to the magnitude of the charges and inversely proportional to the square of the distance between two charges.’ Therefore

            F α ( Q1 × Q2 ) / d2  

            F = k ( Q1 × Q2 / d2 )

Q1 = Magnitude of the charge 1

Q2 = Magnitude of the charge 2

d2 =   Distance between two charges

k =   Constant = 1 / 4πε0εr

Define: Electric field

Electric field

The limited space region around charged body in which an electric charge experiences a force of attraction or repulsion is called an electric field.

Define: Electric lines of force or flux

Flux (Electric line of force)

The electric imaginary field lines around charged body is called as electric lines of flux.

Why electric lines of force do not intersect?       

Electric Lines of Force

The direction of the electric lines of force is from positive charged body to the negative charged body. The electric lines of force do not intersect because at the point of the intersection there are two directions of the field and it is not possible.

Why current does not flow in the dielectric material?        

Dielectric Material

When the potential difference is applied across an insulating material, current does not flow because valance electrons are tightly bound to its nucleus and no free electrons are available for conduction of current.

Define: Electric flux, Electric flux intensity and Electric Potential

Electric flux

The electric field is represented by electric flux lines. The numbers of lines of force eliminating from positive charged particle (or body) is called as electric flux. Its unit is coulomb.

Electric flux intensity

It is defined as electric flux passing through unit area at the right angle to the direction of the field. Its unit is coulomb/meter2


It is defined as force experienced by a unit positive charge placed at that point.

Electric potential

The electrical potential at any point is equal to the work done required to bring a unit positive charge from infinity to that point against the electric field.

Its unit is joule / coulomb.

Define: Electric potential gradient, Electric field intensity and Dielectric Strength  

Electric potential gradient

It is defined as the rate of change of potential with distance. Its unit is volt / meter.

Electric field intensity

It is defined as force experienced by the unit positive charge placed at that point.

Its unit is Newton / coulomb.

Dielectric strength

It is ability of the dielectric material to withstand against breakdown.

The dielectric strength is defined as the maximum potential difference which can withstand by the dielectric material without breakdown of it.

It is expressed in kV / mm.

Explain the term: Induction     


It is phenomenon in which the uncharged body gets charged by proximity charged body.

State the potential of the earth.

The potential of the earth is zero.

Define: Potential       


It is defined as the work done per unit charge.

Define: Factor of safety for dielectric      

Factor of safety

It is defined as the ratio of dielectric strength of insulator to the electric field strength in the dielectric.

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