Electric Charges and Fields Chapter 1 Class 12 Physics Notes Free Download 

Electric Charges and Fields Chapter 1 Class 12 Physics Notes Free Download 

Electric Charges and Fields

Electric charges, Conservation of charge, Coulomb's law-force between two- point charges, forces between multiple charges; superposition principle and continuous charge distribution. Electric field, electric field due to a point charge, electric field lines, electric dipole, electric field due to a dipole, torque on a dipole in uniform electric field. Electric flux, statement of Gauss's theorem and its applications to find field due to infinitely long straight wire, uniformly charged infinite plane sheet and uniformly charged thin spherical shell (field inside and outside). 

Electric charge

It is a property of matter that cause it to experience a force when placed in an electric or magnetic field. Electric charge is a scalar quantity. There are two type of charges + positive and - negative charge.

An object can attain positive charge by loosing electrons while other can attain negative charge by gaining electrons. Like charges repel each other while unlike charges attract each other. Charges always reside on the surface of charged conducting object.An object can be charges by different methods like friction, conduction and induction.

Charges can be added and subtracted as a number.The SI unit is coulomb(C).

Conductors and Insulators

Conductors are those substances which can be used to carry or conduct electric charge/electron from one point to other. They allow electricity to pass through them easily.

e.g. Silver, Copper, iron , Aluminium etc.

Insulators are those substances which cannot conduct electricity. They are also called dielectrics. They offer high resistance to passage of electricity through through them.

e.g. Glass, Rubber, plastic, ebonite, mica etc.

Difference between Dielectrics and Conductors

Dielectrics are non conductors and don't have free electrons at all, while conductors have free electrons in their any volume which make them able to pass the electricity through them.

Charging by Induction

The process of charging a neutral body by bringing a charged body nearby it without making contact between the two bodies is called charging by induction.

Using the process of charging by induction, a conductor may be charged permanently.

Basic properties of Electric Charge

1. Electrive charge is additive in nature. We cxan add them algebrically which is known as principle of superposition of charge. q=q1+q2+q3+..................+qn

2. Charge can neither be created or destroyed. The charge may transferred from one part of system to another, but net charge will always remains the same.

3. Quantisation of electric charge :

The charge on any body can be expressed as an integral multiple of basic unit of charge, i.e. charge on one electron.This phenomenon is called quantisation of electric charge.

It can be written as q = ±ne where n = 1,2,3,.... is any integer, positive or negative and e is the basic unit of charge.

Coulomb's Law

The force of interaction(Attraction or repulsion) between two stationary point charges in vacuum is directly proportional to the product of the charges and inversely proportional to the square of distance between them.

`F = k \frac{q_1q_2}{r^2}`

where k is proportionality constant. K = 1/4π∈₀ = 9 × 10⁹  N m² C^-2

ε₀ = 8.854187817 × 10⁻¹² C² N^-1 m^-² is called permittivity of free space.

One Coulomb is the charge, that when placed at distance 1 m from another charge of same magnitude in vacuum, experiences an electric force of repulsion of magnitude 9 × 10⁹  N. Coulomb is bigger unit so we  use smaller units like mC and µC.