Electrostatics Notes for IIT JEE, Download PDF!

Updated : Dec 9, 2018, 14:00
By : Avinash Kumar

Electrostatics is an important topic from JEE Main / JEE Advanced Exam Point of view. Every year there are 1-3 questions asked from this topic. This short notes on Electrostatics will help you in revising the topic before the JEE Main & IIT JEE Advanced Exam.

You can also download Electrostatics notes in the PDF format through the link shared at the end of this article.

Electrostatics Notes

Electrostatics is the branch of physics which deals with the interaction between the stationary and slow-moving charges and their phenomena.

Electric charges and their conservation:

Electric charge is the one of the fundamental physical property of matter due to it experiences a force when kept in the Electromagnetic field.

There are three types of charged particles every object can possess:

1. Positive charge (Proton)

2. Negative charge (Electron)

3. Neutral (Neutron)

Conservation of charge

For an isolated system, the net charge of the system remains the same. Therefore charge can't be created and can't be destroyed.

Properties of Electric Charge

1. The electric charge (e) is quantized.


2. The like charges repel each other and unlike attract each other.

Coulomb's law

Coulomb's law states that the force acting between two point charges is directly proportional to the product of the magnitude of the charges and inversely proportional to the square of the distance between them.

where  is the constant of proportionality and is the permittivity of free space.

Vector Form of the Coulomb's law is 


The force between multiple Charges

The force between the multiple charges can be found using the superposition principle.

Superposition Principle- According to the superposition principle the net force on any charge due to multiple charges is the vector sum of all the forces acting on that charge due to other charges are taken at a time. The individual forces remain unaffected due to other charges presence.

For n charges the net resultant force due to the principle of superposition.

Continuous Charge Distribution

If the charge is continuously distributed over the surface of the conductor it is known as Continuous charge distribution.  In continuous charge system, a very large numbers of charges are diligently packed and have insignificant space amid them.

There are three types of Continuous charge Distribution:

1. Line Charge distribution When the charge is consistently spread over the length L of a conductor then it is known as linear charge distribution. It is represented by λ, 

2. Surface Charge Distribution When the charge is consistently spread over the surface area of a conductor then it is known as surface charge distribution. It is represented by σ, 

3. Volume Charge Distribution When the charge is consistently spread over the volume of a conductor then it is known as volume charge distribution. It is represented by ρ, 

Electric field and dipole

Electric field- Electric field is defined as the force experienced per unit positive test charge at a point due to any other charge kept in the vicinity. 

Electric field lines- Electric field lines are the hypothetic lines that follow the same direction as the electric field vector at any point. Electric field vector is always tangent to these electric field lines.

The field lines emerge from the positive charge and terminate on a negative charge.

The number of lines drawn leaving a positive charge or approaching a negative charge is proportional to the magnitude of the charge.

No two field lines can cross each other’s path.

Electric Dipole- Electric dipole is a system of two equal in magnitude opposite charges that are separated for a very small distance.

Electric dipole moment: The product of the charge and the separation between them is known as Electric dipole moment. It is a vector quantity which is always directed towards the positive charge.


Electric field due to a dipole

1. On the axial point: Electric field due to the dipole on the axial point P is, 


2. On the equatorial plane: Electric field due to the dipole on equatorial plane at a point P is, 


Torque Experienced by a dipole in a uniform electric field

The magnitude of the torque is experienced by a dipole in a uniform electric field is, 


Electric flux

Electric flux (ΦE)- Electric flux is defined as the number of electric field lines passing through the surface S. It measures the low of electric field through a given area.

For a uniformly charged conductor, the net flux through the closed surface is

 Here θ is the angle between the electric field and the normal component of the area vector.

Gauss’s Law
 Electric flux through the closed surface is defined as the  times the charge closed in the closed surface.

Applications of Gauss’s law

1. Electric field due to an infinitely long straight wire is 



2. Electric field due to the uniformly charged infinite plane sheet is 

3. Electric field due to the uniformly charged thin spherical shell is

Fig (a) The point is outside the shell. (b) The point is inside the shell.


Here R is the radius of the thin spherical shell

Electric Potential and Potential Energy

Electric Potential Energy- It is defined as the work done in moving a charge from one point to the other. 

Electric Potential- It is defined as the change in the Electric potential energy per unit charge.


Electric potential due to a point charge-  The Electric potential due to a point charge at any distance r is 

Electric potential due to a system of charges- For a discrete system of charges the electric potential will use the same principle of superposition. The net potential due to the system of charges is equal to the sum of the sum of the individual potentials.

Electric potential due to an Electric Dipole- Potential due to electric dipole depends on r and on the angle between position vector and dipole moment.

The Potential at any point  form the center of the dipole is

Equipotential Surface- If the charge is uniformly distributed over the surface then the potential at each and every point is same then that surface is considered as an Equipotential Surface.

So the work done to move a charge from one place to other on an equipotential surface is zero. 

Potential energy of a system of two point charge- The energy that results from the collection of charges when the charge will employ a force on any other charge. It is the total amount of work done in moving the charges from an infinite distance to their corresponding positions in the system.

 is the position vector between the charges .

Potential energy of electric dipole in an electric field

As the electric field implies torque in the dipole, the work done in rotating it against the torque is stored in the form of its potential energy.


Conductor, Insulator, and Dielectric

Conductors and Insulators- The materials that allow the free movement if electrons or charge carriers are known as Conductors and the material that avoid any sort of flow of the charged carriers is known as Inductors.

Points to remember

1. The electrostatic field inside an inductor is zero.

2. At the surface of a charged conductor at every point, the electrostatic field is normal to the surface.

3. In the static situation, the interior of a conductor has no excess charge.

4. At the surface of the charged conductor electric field is 

5. The electrostatic field inside a metal cavity is always zero.

Free Charges- Free charges that move throughout the conductor without any constraint. E.g. Electron or ion moving inside a vacuum.

Bound Charges- Bound charge cannot move in response to an external electromagnetic.  E.g. Atoms in an insulator undergoes charge separation when subjected to an electric field, resulting in the formation of dipoles that align themselves to counteract the subjected field.

Dielectric Materials- Dielectric materials are non-conducting substances where the free movement of charges is not possible. The external field induces a dipole moment by re-orienting molecules of the dielectric which in return produces a field that opposes the external field.

Polarisation- Polarization is a phenomenon occurs when an external electric field alters the negative cloud of electrons around positive atomic nuclei in the opposite direction of the applied field. This insignificant separation of charge makes one side of the atom slightly positive and the opposite side somewhat negative.

Thus, Polarization is a comparative shift of positive and negative in opposite directions inside an insulator or dielectric stimulated by an external field.

Polarisation is expressed as  , whereis the constant of dielectric and known as Electrical susceptibility, andis the applied Electric field.

The Electrical susceptibility is also defined the degree of allowance for electric field lines to penetrate into the dielectric.

It can also be expressed in terms relative permittivity  

Capacitor and Capacitance

Capacitor- Capacitor is a two-terminal electrical passive component that used to store the energy in the electrical field.

Capacitance (C) - Capacitance is the ability of a capacitor to store electrical energy is known as its Capacitance. 

, where Q is the charge, and V is the voltage.

The constant C is called the capacitance of the capacitor. It is independent of charge or potential and depends only on the geometrical alignment of the system of two conductors.

Parallel Plate Capacitor: It consists of two large plane parallel conducting plates separated by a small distance and charge is distributed along the conducting surface of the plates.

The capacitance of a parallel plate capacitor is 

Combination of Capacitors

Series Combination-  If two capacitor C1 and C2 are connected in series then the net capacitance is 

If n capacitors are connected in series then the net capacitance is 

Parallel combination- If two capacitor C1 and C2 are connected in parallel then the net capacitance is 


If n capacitor are connected in parallel then the net capacitance is 


Effect of dielectric on capacitance- If a dielectric medium of dielectric constant k is inserted between the plates of the capacitor then the net capacitance of the capacitor is,

where  is the dielectric constant of the material, Co is the capacitance without the dielectric.


Energy stored inside the capacitor- In a capacitor, the work done on moving a positive charge from a negative conductor to a positive conductor against the repulsive forces is stored as energy stored in the plates of the Capacitor.

, where Q is the charge, C is the capacitance of the capacitor.

Van De Graf Generator

Van De Graf Generator is an electrostatic generator that is capable of generating a large static electric potential. It creates a very high electric potential in the order of a few million volts which results in a very large electric field at least until breakdown field of air is reached.

It uses a moving belt that stores charge on a hollow metal structure. The hollow metal structure has a design of a globe which is placed on the top of a column that is insulating in nature. 

Working- A large spherical shell is placed at some height above the ground. An insulating column is fixed which holds it. Two pulleys are coiled with a belt-like insulating material, with one being at ground level and the other one at the center of the shell. The belt carries out a nonstop motion, thus carrying a positive charge constantly from the ground to the top. This belt is kept moving continuously by a motor driving the lower pulley. The positive charge is transferred to the larger shell by a carbon brush, thus coating the outer shell with a very high potential over the time.

Study Notes on Electrostatics, Download PDF!

Moreover, you can also go through the links shared below:

JEE Main Syllabus with weightage

JEE Main Question Paper 2019 with Solutions

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