NCERT Solution Class 12th Physics Chapter – 1 Electric Charges and Fields Notes

NCERT Solution Class 12th Physics Chapter – 1 Electric Charges and Fields

NCERT Solution Class 12th Physics Chapter – 1 Electric Charges and Fields

?Chapter – 1?

✍Electric Charges and Fields✍

?Notes?

The charge on an electron and proton is called a fundamental charge.

Electric charge is quantized and charge on a body can be expressed as, q = ± ne, where n is an integer and e = 1.6 × 10^-19 C.

The minimum value of the dielectric constant is 1 for free space.

The maximum value of the dielectric constant is infinity for conductors i.e., metals.

A dielectric constant is a dimensionless number as it is the ratio of two similar quantities.

Electric charge is a scalar quantity.

Electric charge obeys the law of conservation of charge.

It is always additive in nature.

Coulomb’s law in vector form is more informative than in its scalar form.

The electrostatic force is a central force as it acts along the line joining the centers of two charges.

The electrostatic force is Newtonian force i.e., obey’s Newton’s third law of motion.

Static electricity or frictional electricity on bodies occurs mainly due to the transfer of electrons from one body to another body.

1 C = 3 × 10⁹ stat Coulomb.

Stat Coulomb is the C.G.S. unit of charge. It is also called an electrostatic unit (e.s.u.) of charge.

S.I. unit of the electric field is NC^-1.

The dielectric constant is also known as the relative permittivity of the medium (sr).

Two equal and opposite charges separated by a finite distance constitute an electric dipole.

S.I. Unit of dipolemoment is Coulomb metre (Cm).

Electric dipole moment is a vector quantity acting from – q to + q charge.

In a uniform electric field, the net force on the dipole is zero and it experiences a torque only,

In a uniform electric field, a dipole has only rotatory motion.

In a non-uniform electric field, the dipole experiences both torque and force, hence it has rotatory as well as translatory motion.

Electric lines of force never intersect each other. They always leave or enter the surface of the conductor perpendicularly.

The electric field inside a charged or uncharged conductor placed in an external field is always zero.

Electric flux is a scalar quantity and its S.l. unit is Nm^-2 C^-1.
The electric field is maximum at the surface of a charged spherical shell and zeroes inside it.

The electric field due to a cloud of charge or due to a solid charged sphere is maximum at its surface and varies with distance from its center as:

Electric field lines are perpendicular to the equipotential surface.

The surface of a charged conductor is an equipotential surface.

Coulomb’s law is valid only for point charges.

The electric charge does not change with velocity.

No point charge produces an electric field at its own location.

Electric charge resides only on the outer surface of a conductor.

Coulomb’s force between two charges is independent of the presence of other charges.

E is independent of the shape of the conductor.

E at a point on the surface of a conductor is directly proportional to the surface density of charge at that point.

Eat the center of a charged circular ring is always zero.

Coulomb’s law in electrostatics – Two-point charges attract or repel each other with a force directly proportional to the product of the magnitude of charges and inversely proportional to the square of the distance between them.

Frictional electricity – Electricity produced on bodies when they are rubbed against each other.

Additive nature, of charge – Total charge on an isolated system is equal to the algebraic sum of all individual charges of the system.

Law of conservation of charge – Total charge on an isolated system always remains conserved.

Principle of superposition – It states that the total force on a given point charge due to other interacting charges is the vector sum of the forces applied by the individual charges on it.

Test charge – It is a small +ve charge. It is denoted by q0.

Electric field – It is defined as the space around a point charge in which its effect can be felt.
Or
It is the limiting value of electrostatic force per unit test charge

Electric dipole – It is a system of two equal and opposite charges separated by a finite distance.

Electric dipole moment – It is defined as the product of magnitude. of either charge and the dipole length.

Electric line of force – It is defined as the path straight or curved tangent at every point of which gives the direction of the electric field.

Electric flux (Φ) – It is defined as the total number of electric lines of force passing through an area held normal to them around a given point.

Gauss’s law or Theorem – It states that the electric flux through a 1/ε₀ closed surface is: times the total charge enclosed inside it.

Gaussian Surface – It is defined as any closed surface around the charge distribution enclosing some charge in it.

Important Formulae –

Electric field due to a point charge q is given by

Electric field at a point on the axis at a distance x from centre of a
charged circular coil of radius r having charge q centre is given by
alongitsaxis.

Electric field at a point on the axial line of an electric dipole at a distance r from its centre is given by

Electric field at a point on the equitorial line of an electric dipole at a distance r from its centre is given by

Torque on an electric dipole in a uniform  is

or
τ = pE sin θ
where θ is the angle betweenand .

Force on a charge due to n other charges is

Electric flux, =
When dS−→ is the area vector acting alòng outward drawn normal.

Φ = ∮_s E→ dS−→ = q/ε₀

Electric field at a point due to an infinitely long straight conductor or wire of linear charge density is
E = 1/2πε₀–  λ/r
where r = perpendicular distance of the point from the wire,

E due to an infinite plane sheet ol charge having surface charge density c is given by
E = σ/2ε₀

E between two plane parallel sheets of charge is given by
E = σ/ε₀

When σ = surface charge density.
R = radius of shell.

at a point due to a solid sphere of radius R volume charge density p at a point at a distance r is given by