NEET Study Notes for Electrostatics: Electrostatics is defined as the study of stationary or slow-moving electric charges. Some phenomena in which we can observe electrostatics are- Laser machine and photocopier, grain silos explode spontaneously, Paper is attracted to a charger scale. Some important topics in Electrostatics include- Electric charges, electric field, electric flux, conductors, and insulators.

• Electrostatics is an important unit in NEET Physics Syllabus with around 3-4 questions expected.
• As per the previous year’s analysis, the questions from Electrostatics in NEET 2022 will be of a moderate difficulty level. NEET Study Notes for electrostatics and sample questions will help you to score well.

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Important Topics in NEET Electrostatics

Electric charge

When a force is experienced by matter in the electromagnetic field, such a charge that flows through is known as an electric charge. The movement of electric charge in the electric field leads to the generation of a magnetic field. This interaction of charges leads to the formation of the electromagnetic field.

Electric charges are positively charged or protons and negatively or electrons. Neutrons have zero charges

Electric charge is measured by Q=IT

where Q is the electric charge

I is the electric current and t is the time

S.I unit of electric charge is coulomb

Read:

• NEET Study Notes on Ray Optics
• NEET Study Notes on Wave Optics

Conservation of Charge

The net charge of a system does not change in an isolated system, This means that charge can neither be created nor can it be destroyed. Electric charge can be quantized

where Q= ne

e is 1.602 *10-19 coulomb

where the like charges repel and unlike charges attract

Coulumb’s Law

The force that acts between two charges is directly proportional to the product of the magnitude of charges and inversely proportional to the square of the distance between them.

It can be represented mathematically as

 

where the constant of proportionality is 

Permittivity of free space is 

Vectors form of coulomb's law is 

Superposition Principle

Superposition principle is used to determine the force between multiple charges. As per the superposition principle, in space, every charge produces an electric field. This electric field does is not affected by other charges of the medium. The electric field that is created is thus sum of the electric field of other charges.

By taking into consideration the superposition principle, the net resultant force due to multiple charges is

  

Continuous Charge Distribution

The phenomenon of charge getting distributed over a conductor’s surface is called Continous charge distribution. There is no significance of space and charge in this system. Continous Chrga distribution can be classified into;

• Linear Charge distribution- Charge that is evenly distributed over a conductor is called Linear charge distribution.

• Area/Surface charge distribution- Charge that is evenly distributed over the surface of a conductor is called Surface charge distribution.

• Volume Charge Distribution- Charge that is evenly distributed over the volume of the conductor is called volume charge distribution.

Electric Field

Electric Field is defined mathematically as the vector field in consideration with each point of space, and the force that is exerted per unit charge on a positive test charge at a specific point.

 

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Electric Dipole

The system of two equal and opposite charges in magnitude, which is separated by a small distance Electric Dipole Moment is a vector quantity. It is the product of charge and the distance between them.

Electric Field due to dipole

Due to dipole, Electric field moments are:

• On Axial Point- On Axial point p, electric field due to dipole is 
• Equatorial Plane- On the equatorial plane at point P, the electric field is 
• In a uniform centric field, torque experienced by a dipole is 

Electric Flux

Electric Flux is the number of electric lines of force that crosses the surface normal to an area.

The product of area and field in scalar quantities is defined as an electric field through an elementary area

  p=EA

Electric Flux is maximum when an electric field is normal to the area

When the field is parallel to the area electric flux will be minimum

In a closed surface, the inward flux will be negative while outward flux is positive.

Electric Potential

The amount of work done that is responsible for taking a unit positive test charge from infinity to the point along any path is known as the Electric Potential or the electrostatic potential. It is denoted by V

Electric Potential is a scalar quantity where the S.I unit is volt.

Electric potential due to a point charge q at separation r is

Electric Potential due to multiple charges

Electric potential due to multiple charges q1, q2… qn will be

V= V1+V2..+Vn

Relationship between Electric Field and Potential

The relationship between electric field and potential is

where E is the electric field

V is the potential difference

Must Read:

• NEET Study Notes on Laws of Motion
• NEET Study Notes on Planar Motion

Equipotential Surface

The surface where the potential is same on any point is known as the Equipotential surface. Work is not done from one to another on an equipotential surface. Electric lines of force and equipotential surface are perpendicular to each other.

In the case of Hollow Charged sphere:

• At any point inside the sphere, intensity is zero.
• At an point on the surface, intensity is maximum and equal to 
• In vector form, the electric field intensity is represented by

  

In the case of a Solid charged sphere

The potential outside the sphere and at any point inside the sphere is equal.

The potential is indirectly proportional to the distance from the point of the center is an equipotential surface.

  

Electron Volt

The unit of energy in particles is called Electron volt. It can be represented as eV.

1 eV is equal to 1.602×10‑19 J.

Charged particles in an electric field

In an electric field, when the direction of the positive test is also in the same direction the acceleration of charged particle increases, there is an increase in kinetic energy, decrease in potential energy. The speed of acquired is

 

where m is the mass of charged particle

q is the charge carried

V is potential

Electric Lines of Force

In the line of force, a unit positive charge, moves in the electric field. The direction of the field is determined where there is the tangent of a point to the line of force.

• Two electric lines of force do not intersect.
• The strength of the field at a point and the number of lines that pass through a unit area are equal.
• Electric lines of force are not in closed loops.

Conductors, Insulators, and Semiconductors

• Conductor is the body in which electric charge can flow easily. Examples of conductors are metals.
• Insulators are also called dielectric and electric charge does not flow through them. Examples- rubber, plastics, glass, wool, etc.
• The intermediate bodies between conductors and insulators are called semi-conductors. Exaample silicon, germanium etc.

Read NEET Study Notes on Current Electricity

Dielectric Strength

The insulating property of an insulator can be broken by applying Dielectric strength. It is the minimum amount of field intensity. The size and dielectric strength of the medium affect the maximum charge that can be held by a sphere.

Dielectric strength of air is 3 106 V/m

Dielectric strength of Teflon is 60 ×106 Vm-1

Van de Graff Generator

Robert J. Van Graaff invented an electrostatic generator, called a Van de Graaff generator. In this, a moving belt is used to accumulate charge on a hollow metal structure. This is in a sphere structure on the top of the insulating column.

A large electric field is created due to the high electric potential. This electric field is used for the acceleration of charged particles.

• In the above figure, there is a higher potential in the inner sphere. It gets accumulated on the surface due to independence from the charge Q. Difference in potential V (r) - V(R) is positive. This potential is due to the charge being constant up to the radius. Thus there is a cancellation of difference.
• A conducting wire connects the small and large spheres and this leads to the transfer of charge from the small sphere to the bigger sphere. There is an increase in charge on the larger sphere if the small charged sphere enters the large sphere.
• Similarly, as the charge increases, potential in the large sphere also increases. This will remain so till we reach a position of the breakdown of air. The principle of working of Van De Graaff is similar.

NEET Sample MCQs on Electrostatics

Question: What is the potential inside a hollow sphere that is charged?

1. Same as that on surface
2. Less than the surface
3. Zero
4. None of these

Answer: Same as on the surface

Question: The force between electric charges is stated by which law?

1. Ampere’s Law
2. Faraday’s Law
3. Ohm’s Law
4. Coulomb's Law

Answer: Coulumb’s Law

Question: Name the law states that the total flux out of a closed surface is equal to the net charge within the surface.

1. Gauss’s Law
2. Laplace’s Law
3. Coulomb's Law
4. Gaussian’s Law

Answer: Gauss’s Law

Question: Which amongst the following is not a characteristic of magnetic flux.

1. There is no physical existence of magnetic flux lines
2. Magnetic flux lines are in a closed-loop
3. Magnetic flux lines in opposite directions repel each other
4. Magnetic flux lines in opposite directions attract each other

Question: Electric field strength of a charge—-

1. Decreases with the square of distance
2. Decreases with the cube of distance
3. Decreases with distance
4. Increases with distance

Answer: Decreases with the square of the distance

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