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# NCERT Solutions for Class 12 Physics Chapter 1 - Electric Charges and Fields – Free PDF Download `

Electric Charges and Fields, is the very first chapter of NCERT physics for class 12. In this chapter we are going to study about electric charges, conductors and insulators, basic properties of charges and many more which we will discuss later in this page. The NCERT Solutions for Class 12 Physics Chapter 1 Electric Charges and Fields provided here to help you prepare well for your Class 12 Board exam, as well as competitive exams like JEE and state level exams. Here, in these class 12 ch 1 physics ncert solutions, you can find solved answers for chapter 1 Electric Charges and Fields from Class 12.

These class 12 physics ncert solutions chapter 1 electric charges and fields, will also help you go through the basics, and you should expect at least one question in your board exam from this chapter. You can download these solutions at free of cost on our eSaral website.

## Subtopics of Class 12 Physics Chapter 1 Electric Charges and Fields

1. Introduction

2. Electric Charge

3. Conductors and Insulators

4. Charging by Induction

5. Basic Properties of Electric Charge

• Charge is Conserved

• Quantisation of Charge

6. Coulomb’s Law

7. Forces between Multiple Charges

8. Electric Field

• Electric Field Due to a System of Charges

• The Physical Significance of the Electric Field

9. Electric Field Lines

10. Electric Flux

11. Electric Dipole

• The Field of an Electric Dipole

• The Physical Significance of Dipoles

• Dipole in a Uniform External Field

12. Continuous Charge Distribution

13. Gauss’s Law

14. Applications of Gauss’s Law

15. Field Due to an Infinitely Long Straight, Uniformly Charged Wire

• Field Due to a Uniformly Charged Infinite Plane Sheet

• Field Due to a Uniformly Charged Thin Spherical Shell

### Electric Charge

In an atom, an electrical charge occurs whenever the number of protons in the nucleus differs from the number of electrons surrounding the nucleus. If the number of electrons are more than the number of protons then the atom has a negative charge. If the number of electrons are less than the number of protons then the atom has a positive charge.

In this chapter you will learn about various experiments; It was noticed that if two glass rods rubbed with wool or silk cloth are brought close to each other, they repel each other. The two strands of wool or two pieces of silk cloth, with which the rods were rubbed together, also repel each other. Although, the glass rod and wool attracted each other.

### Conductors and Insulators

Those materials which allow electricity to pass through them easily are called Conductors. They have electric charges (electrons) that are comparatively free to move inside the material or substance. Metals, human and animal bodies and earth are conductors.

Those materials which do allow electricity to pass through them are called insulators. The atoms of the insulator have tightly packed electrons which cannot move freely.

### Basic Properties of Electric Charge

In this topic you will get to know about the properties of Electric charges. We have noticed that there are two kinds of charges, namely positive and negative and their effects tend to cancel each other.

If a system contains two point charges one is q1 and another is q2, the total charge of the system is obtained simply by adding algebraically q1 and q2 , i.e., charges add up like real numbers or they are scalars like the mass of a body. If a system contains n charges q1, q2, q3, …, qn, then the total charge of the system is q1 + q2 + q3 + … + qn, this is called additivity of charges.

### Charge is conserved

When bodies are charged by rubbing, there is transfer of electrons from one body to the other body; no new charges are either created or destroyed.  When we rub two bodies, what one body gains in charge the other loses the charge. Within an isolated body consisting of many charged bodies, due to interactions among the bodies, charges may get redistributed but it is found that the total charge of the isolated system is always conserved. This phenomena is called Conservation of charge.

### Quantisation of Charge

All free charges are integral multiples of a basic unit of charge which is denoted by e. Hence, charge q on a body is always followed by

q = ne

where n is a type of integer, either positive or negative. This unit of charge is the charge that an electron or proton carries. By convention, the charge on an electron is taken to be negative; therefore charge on an electron is written as –e and that on a proton as +e.

### Coulomb’s Law

Coulomb states that the force between two point charges and found that it varied inversely as the square of the distance between the charges and was directly proportional to the product of the magnitude of the two charges and acted along the line joining the two charges.

### Forces between Multiple Charges

It's Proven that force on any charge due to a number of other charges is the vector sum of all the forces on that charge due to the other charges, taken one at a time. The individual forces are not affected due to the presence of other charges.

### Electric Field

Electric fields are produced by electric charges, which can be either positive or negative.The substances who have similar charges repel each other, while opposite charges attract each other. When a charged particle is placed under an electric field, it experiences an electric force due to the interaction with the electric field lines.

### Electric Field Lines

An electric field line is an imaginary line or curve that is drawn from a point of an electric field in such a way that tangent to it at any point gives the direction of the electric field at that point.

Properties of Electric Field Lines

1. Electric field lines start from positive charge and end at a negative charge point.

2. The number of field lines that start or end at a charge is proportional to the magnitude of the charge.

### Electric Flux

The total number of electric field lines passing a particular given area in a unit of time is defined as the electric flux.

### Electric Dipole

An electric dipole is a pair of equal and opposite point charges +q and –q, separated by a small distance 2a. The line connecting the two charges is defined as a direction in space. By convention, the direction from –q to +q is said to be the direction of the dipole and the mid-point of locations of –q and q is called the centre of the dipole.

#### The Field of an Electric Dipole

The electric field of the pair of charges –q and +q at any point in space can be found out from Coulomb’s law and the superposition principle. The results are simple for the following two cases

1.  when the point is on the dipole axis, and
2.  when the point is in the equatorial plane of the dipole

#### The Physical Significance of Dipoles

In most of the substance, the centers of positive charges and of negative charges lie at the same place. Therefore, the dipole moment  of these substances is zero like CO2 and CH4 are of this type of molecules.

But in some molecules, the centers of negative charges and of positive charges do not collide. Hence, they have a permanent electric dipole moment, even if electric field is not there.These molecules are known as polar molecules.H2O, Water molecules, is an example of this type.

#### Dipole in a Uniform External Field

Let us consider a permanent dipole of dipole moment p in a uniform external field E.There is a force qE on q and a force –qE on –q. The net force on the dipole is zero, as E is uniform. Therefore, the charges are separated, so the forces act at different points, resulting in a torque on the dipole. When the net force is zero, the torque (couple) is independent at the origin.

## Gauss’s Law

Gauss law states that the total electric flux out of a closed surface is equal to the charge enclosed divided by the conductivity. The electric flux in an area is defined as the electric field multiplied by the area of the surface projected in a plane and perpendicular to the field.

### Application of Gauss’s Law

Following are the application of Gauss’s Law

1. In the case of a charged ring of radius R on its axis at a distance x from the center of the ring.

2. In the case of an infinite line of charge, at a distance, ‘r’.

3. The intensity of the electric field near a plane sheet of charge

4. The field between two parallel plates of a condenser

## Key Features of NCERT Solutions for Class 12 Physics Chapter 1 Electric Charges And Fields

If you are seeking the NCERT solutions for Class 12 Physics Chapter 1 Electric Charges And Fields  find it helpful for various reasons.

1. The solutions of questions are updated according to the latest NCERT guidelines.

2. All the solutions to the theoretical and numerical questions are provided in a simple and easy way.

3. Each and every question is explained by experienced teachers of eSaral.

All the solutions are designed to help you to develop a better understanding of the concepts of Electric Charges and Fields. If you want to excel in this field of Physics, you can download and find assistance in the NCERT Solutions for Class 12 Physics Chapter 1 for free in pdf form.

#### FAQs

Question 1 : Explain Coulomb’s law covered in Chapter 1 Electric Charges And Fields of NCERT Solutions for Class 12 Physics.

Answer : Coulomb's law states that, the force of repulsion or attraction between two charged bodies is directly proportional to the product of their charges and inversely proportional to the square of the distance between them. It acts along the line joining the two charges considered to be point charges.

Question 2 : What are the main topics covered in Chapter 1 Electric Charges and Field of NCERT Solutions for Class 12 Physics?

Answer : The main topics covered in Chapter 1 Electric Charges and Field of NCERT Solutions for Class 12 Physics are mentioned as follows:

1. Introduction

2. Electric Charge