Electric Charges And Fields:Class 12 Physics NCERT Chapter 1

Key Features of NCERT Material for Class 12 Physics Chapter 1 – Electric Charges and Fields 

In these Chapter 1: Electric charges and fields we will learn about forces between two charged particles and their properties.In the next Chapter 2:Electrostatic Potential and Capacitance we will learn potential energy of the system of charges

Quick revision notes

1. Electric Charge Charge is the property related with issue because of which it creates and encounters electric and attractive impact. 
2. Conductors and Insulators Those substances which promptly permit the entry of power through them are called conductors, for example metals, the earth and those substances which offer high protection from the entry of power are called protectors, for example plastic pole and nylon.
3. Transference of electrons is the reason for frictional power. 
4. Additivity of Charges are scalars and they include like genuine numbers. It implies if a framework comprises of n charges q1, q2, q3 , … ,qn, at that point all out charge of the framework will be q1 +q2 + … +qn. 
5. Conservation of Charge The absolute charge of a confined framework is constantly saved, for example beginning and last charge of the framework will be same. 
6. Quantisation of Charge Charge exists in discrete sum as opposed to persistent worth and henceforth, quantised. 

Numerically, charge on an article, q=±ne 

where, n is a number and e is electronic charge. At the point when any physical amount exists in discrete parcels instead of in consistent sum, the amount is supposed to be quantised. Thus, charge is quantised. 

7. Units of Charge

(i) SI unit coulomb (C)

(ii) CGS system

(a) electrostatic unit, esu of charge or detail coulomb (detail C) 

(b) electromagnetic unit, emu of charge or stomach muscle C (stomach muscle coulomb) 

1 stomach muscle C = 10 C, 1 C = 3 x 109 detail C 

8. Coulomb’s LawIt expresses that the electrostatic power of communication or repugnance acting between two fixed point charges is given by

8. Electrostatic forces (Coulombian forces) are conservative forces.
9. Principle of Superposition of Electrostatic Forces This rule expresses that the net electric power experienced by a given charge molecule q0 because of an arrangement of charged particles is equivalent to the vector aggregate of the powers applied on it because of the apparent multitude of other charged particles of the framework. 

8. Electrostatic Force due to Continuous Charge Distribution

The district where charges are firmly dispersed is said to have nonstop appropriation of charge. It is of three kinds given as beneath: 

12. Electric Field Intensity The electric field power anytime because of source charge is characterized as the power experienced per unit positive test charge put by then without upsetting the source charge. It is communicated as

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

12. Electric Field due to a System of Charges

Same as the instance of electrostatic power, here we will apply rule of superposition, for example 

15. Electric Field LinesElectric field lines are a method of pictorially planning the electric field around a setup of charge(s). These lines start on certain charge and end on negative charge. The digression on these lines anytime provides the guidance of field by then. 
16. Electric field lines due to positive and negative charge and their combinations are shown as below:

15. Electric Dipole Two point charges of same extent and inverse nature isolated by a little separation by and large structure an electric dipole. 
16. Electric Dipole Moment The quality of an electric dipole is estimated by a vector amount known as electric dipole second (p) which is the result of the charge (q) and partition between the charges (2l). 

15. Electric Field due to a Dipole Electric field of an electric dipole is the space around the dipole wherein the electric impact of the dipole can be experienced. 

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

15. Dipole is in stable harmony in uniform electric field when edge among p and E is 0° and in unsteady balance when edge θ= 180°. 
16. Net power on electric dipole set in a uniform electric field is zero. 
17. 26. There exists a net power and force on electric dipole when set in non-uniform electric field. 
18. 27. Work done in turning the electric dipole from θ1 to θ2 is W = pE (cos θ1 – cos θ2) 
19. 28. Likely vitality of electric dipole when it pivots from θ1 = 90° to θ2 =0 

U = pE (cos 90° – cosθ) = – pE cos θ = – p .E 

29. Work done in turning the dipole from the situation of stable balance to flimsy harmony, for example when θ1 = 0° and θ2 = π. 

W = 2 pE 

30. Work done in turning the dipole from the situation of stable harmony to the situation in which dipole encounters greatest force, for example when θ1 = 0° and θ2 = 90°. 

W = pE

(Chapter 1: Electric charges and fields)