Class 12 Physics Ch 1


Electric Charges and Fields Class 12 Notes Chapter 1

Chapter 1: Electric Charges and Fields, NCERT Solutions for Class 12 Physics
In addition to reading the theory of this Chapter 1 Electric Charges and Fields before tackling the NCERT questions, our experienced and well-respected teachers of Physics Wallah have prepared NCERT Solutions for Class-12 Physics Chapter 1 Electric Charges and Fields. Physics Wallah's NCERT Solutions for Class 12 Physics are available for download and sharing.
Electric Charges and Fields, Chapter 1

The NCERT Solutions for Class 12 Physics Chapter 1, Electric Charges and Fields, are designed to aid students in their preparation for the Class 12 CBSE Board exam and competitive exams such as JEE. These solutions provide solved answers for Electric Charges and Fields from Class 12, as well as important questions from previous year question papers, exemplary problems, MCQs, worksheets, and exercises. These solutions will also help students grasp the fundamentals, and it is recommended that they practice these solutions to prepare their Class 12 Notes. The PDF of NCERT Solutions for Class 12 Physics Chapter 1 can be downloaded from the link below.


CBSE Class 12 Physics Chapter 1 Point Wise Notes

1. Electric Charge Charge is a characteristic of matter that causes it to produce and feel magnetic and electric effects.
2. Insulators and Conductors Conductors are materials that easily let the flow of electricity through them, such as metals and the ground, while insulators are materials that offer strong resistance to the flow of electricity, such as nylon and plastic rod.
3. Frictional electricity is caused by electron transfers.
4. Additivity of Charges Charges are scalars and they add up like real numbers. It means if a system consists of n charges q1, q2, q3 , … ,qn, then total charge of the system will be q1 +q2 + … +qn.
5. Conservation of Charge The total charge of an isolated system is always conserved, i.e. initial and final charge of the system will be same.
6. Quantisation of Charge Charge exists in discrete amount rather than continuous value and hence, quantised.
Mathematically, charge on an object, q=±ne
where, n is an integer and e is electronic charge. When any physical quantity exists in discrete packets rather than in continuous amount, the quantity is said to be quantised. Hence, charge is quantised.
7. Units of Charge
(i) SI unit coulomb (C)
(ii) CGS system
(a) electrostatic unit, esu of charge or stat-coulomb (stat-C)
(b) electromagnetic unit, emu of charge or ab-C (ab-coulomb)
1 ab-C = 10 C, 1 C = 3 x 109 stat-C
8. Coulomb’s Law It states that the electrostatic force of interaction or repulsion acting between two stationary point charges is given by

9. Electrostatic forces (Columb forces) are conservative forces.
10. Principle of Superposition of Electrostatic Forces This principle states that the net electric force experienced by a given charge particle q0 due to a system of charged particles is equal to the vector sum of the forces exerted on it due to all the other charged particles of the system.

11. Electrostatic Force due to Continuous Charge Distribution
The region in which charges are closely spaced is said to have continuous distribution of charge. It is of three types given as below:

12. Electric Field Intensity The electric field intensity at any point due to source charge is defined as the force experienced per unit positive test charge placed at that point without disturbing the source charge. It is expressed as

13. Electric Field Intensity (EFI) due to a Point Charge.

14. Electric Field due to a System of Charges
Same as the case of electrostatic force, here we will apply principle of superposition, 

15. Electric Field Lines Electric field lines are a way of pictorially mapping the electric field around a configuration of charge(s). These lines start on positive charge and end on negative charge. The tangent on these lines at any point gives the direction of field at that point.
16. Electric field lines due to positive and negative charge and their combinations are shown as below:

17. Electric Dipole Two point charges of same magnitude and opposite nature separated by a small distance altogether form an electric dipole.
18. Electric Dipole Moment The strength of an electric dipole is measured by a vector quantity known as electric dipole moment (p) which is the product of the charge (q) and separation between the charges (2l).

19. Electric Field due to a Dipole Electric field of an electric dipole is the space around the dipole in which the electric effect of the dipole can be experienced.

21. Torque on an electric dipole placed in a uniform electric field (E) is given by

24. Dipole is in stable equilibrium in uniform electric field when angle between p and E is 0° and in unstable equilibrium when angle θ= 180°.
25. Electric dipoles in a consistent electric field exert no net force.
26. When put in a non-uniform electric field, an electric dipole experiences a net force and torque.
Work was done to turn the electric dipole from position 1 to position 2.Three identical capacitors connected in parallel have a 12 microfarad net capacitance. When two of them are connected in (i) parallel (ii) series, what would the net capacitance be?
Over a metal sphere with a radius of R, a charge of Q is dispersed. What are the electric potential and field at the center? E = 0 and V equals kQ/R.
When two places are the same distance apart from the dipole's center, calculate the ratio of the electric field intensity caused by the dipole at a position on the equatorial line to the field at a point on the axial line.
A charged insulated conductor B is brought close to an uncharged conductor A that has been set up on an insulating stand. What happens to B's potential and charge?
A charged particle Q goes from point A to point B in the direction of a uniform electric field of strength E before returning from point B to point A. Calculate the amount of effort the electric field did to move the charge particle from point A to point B and vice versa.
How does a conductor's temperature change affect an electron's relaxation time inside it?

Why is a potentiometer used over a voltmeter to measure a cell's emf?
The length of a copper wire with resistance R is uniformly stretched until it has multiplied by n. What new resistance will it face?
A automobile battery has a 12V voltage. Eight dry 1.5 V cells connected in series also produce 12V, although such a setup is not employed to start a vehicle. Why?
A mass m oil drop with a charge Q must be kept stationary in the earth's gravitational field. What electrostatic field strength and direction is necessary for this task? E = mg/Q, downward is the solution.

Importance of Class 12 physics Chapter Electric Charges and Fields 
Chapter 1 of Class 12 Physics, is an important study material for the Students who are presently studying in CBSE 12th standard. The NCERT Results for Class XIIth physics Quick Revision
 titled Electric Charges, has been meticulously crafted in accordance with the latest CBSE Syllabus 2023-24. The NCERT Solutions for this chapter delve into the calculation of forces between two charged particles placed at a specific distance from each other. Additionally, we explore the phenomenon of charge generation in materials through friction, such as when a glass rod is rubbed with a silk cloth. Furthermore, we investigate the rationale behind disregarding the quantization of charge in the context of large-scale charges. Discover more on this topic here.

Class 12 Physics poses a challenge for numerous students who encounter difficulty in achieving a satisfactory score in the CBSE Board examinations. To attain commendable marks, it is recommended that students refer to the NCERT Solutions presented herein. This will instill the requisite confidence in students by acquainting them with the question types that feature in the board examination.