A charge is a property associated with matter. It is due to electric charge that matter produces and experiences electric and magnetic effects. They can be of the following types:

• Unlike charges: They are charges that repel each other.
• Like charges: They are charges that attract each other.

• Conductors are substances that readily allow the passage of electricity through them. They include metals, the earth, etc.
• Insulators are substances that offer high resistance to the passage of electricity. They include plastic rods and nylon.

Induction is a charging method in which an object gets charged without actually contacting another charged object. This charging method necessitates a thorough grasp of the nature of a conductor as well as the idea of polarization.

• The transference of electrons is the source of frictional electricity.
• The properties of electrical charges include the following:
• Additivity of Charges:
• Here, charges are considered as scalars and they can be added up like real numbers.
• For example, if a system consists of n charges q1, q2, q3, … , qn, then the total charge of the system will simply be the sum of the individual charges which is q1 +q2 + … +qn.
• Conservation of Charge:
• This states that the total charge of an isolated system is always conserved.
• Thus, the initial and final charge of the system will be the same.
• Quantisation of Charge:
• Charges exist in discrete and quantifiable amounts.
• It is not a continuous value. Hence, it is quantised.
• Mathematically, the charge on an object can be represented as q=±ne
• Here, the following are the denotations:
• n is an integer
• e is the electronic charge
• A physical quantity is said to be quantised when it exists in discrete packets (such as charges) rather than continuous amounts.

It states that the electrostatic force of interaction or repulsion acting between two stationary point charges is given by the following formula:

Here, the following are the denotations:

• Eo is the permittivity of free space which has a value of 8.85 x 10-12 C2 / Mn2
• Q denotes the charges
• E is the absolute permittivity

Principle of Superposition of Electrostatic Forces: The net electric force experienced by a particular charge particle q0 as a result of a system of charged particles is equal to the vector sum of the forces exerted on it by all the other charged particles in the system.

An electric field is a physical field that surrounds electrically charged particles. It exerts a force on the surrounding charged particles. Thus, it either attracts or repels them.

The following are some of the properties of electric field lines:

• Electric field lines are endless curves that have no ends. Thus, they can’t form closed loops.
• The electric field lines intersect each other at infinity.
• They begin from positive charges and terminate at negative charges.

The force experienced per unit positive test charge put at that location without disrupting the source charge is defined as the electric field intensity at any point owing to source charge. It is expressed as

E = Lim (q0 → 0) F / q0

• Electric field lines are a pictorial representation of the electric field around a configuration of charge or charges.
• These lines begin from a positive charge and terminate on a negative charge.
• Drawing a tangent on these lines at any point gives the direction of the field at that point.

• Electric flux is a mode measure of an electric field through a given surface.
• It's a way of describing the intensity of an electric field at any distance from the charge that's causing it.

A dipole is made up of two point charges of equal size and opposing nature separated by some distance.

Electric Dipole Moment:

• It is a measure of the strength of an electric dipole in terms of a vector quantity.
• It is denoted as p.
• It is calculated as the product of the charge (q) and separation between the charges.

P = q x 2l

A . The field of an electric dipole

• P = qd which is the magnitude of the charges multiplied by the distance between the two.

B . The physical significance of dipoles

• Dipoles are very important for the study of the electrical behaviour of matter.
• Matter consists of molecules that are electrically neutral and these molecules may be polar or nonpolar.

C . Dipole in a uniform external field

• The dipole experiences a torque.

• Continuous charge distribution is a system in which charges are uniformly distributed over a conductor.
• In this system, infinite numbers of charges are closely packed. Thus, they have minor space between them.

Gauss’s law states that the total electric flux out of a Gaussian surface is the sum of the net charge enclosed in that surface divided by the permittivity of empty space.

• Electric field due to an infinite long straight charged wire
• Electric field due to an infinite charged plane sheet
• Electric field due to two parallel charged sheets
• Electric field due to a uniformly charged spherical shell
• Electrostatic shielding: This is a process of isolating a specific region of space from an external field. 

• Let us consider a uniformly charged wire of infinite length having a constant linear charge density, λ. This is the charge per unit length.
• P is the point at a distance r from the wire.
• E is the electric field at point P.
• A cylinder of length l and radius r closed at either end by plane caps normal to the axis is chosen as a Gaussian surface.
• Consider a very small area ds on the Gaussian surface.
• By symmetry, the magnitude of the electric field will be similar at all points on the curved surface of the cylinder and directed radially outward.
• Thus, by Gauss law: E = λ / 2piEor

1. The electrostatic force on a small sphere of charge 0.4 µC due to another small sphere of charge –0.8 µC in the air is 0.2 N.

(a) What is the distance between the two spheres?

(b) What is the force on the second sphere due to the first?

Answer:

Formula: F = q1q2/ 4piEor2

F = 0.2

Thus, r = 0.12m

2. Answer the following questions:

(i) Explain the statement ‘electric charge of a body is quantised’.

(ii) Why can one ignore quantisation of electric charge when dealing with macroscopic, i.e., large scale charges?

Answer:

(i) The statement ‘electric charge of a body is quantised’ means that only integrals like 1, 2, …n numbers of electrons can be transferred from a body to another. Charges cannot be transferred in their fractions. Thus, the total charge possessed by a body is only in integral multiples of the electric charge.

(ii) When it comes to big scale or macroscopic charges, the charge that is employed is disproportionately enormous in comparison to the magnitude of the electric charge. As a result, on a macroscopic level, charge quantisation is useless. As a result, it is disregarded, and the electric charge is assumed to remain constant.

1. Is the NCERT Solutions for Class 12 Physics Chapter 1 sufficient for exam preparation?

The solutions provided in the NCERT solutions textbook of class 12 physics can help clarify doubts, improve performance, and score extremely well during exams. Students can likewise begin practising more from NCERT Solutions Class 12 physics that can assuredly result in improved performance. This book is more than sufficient if practised properly and regularly.

2. How do I develop Numerical Solving ability in Physics?

The following steps can be taken by students to master numerical solving in physics:

• Focus and establish a clear mental image of the problem.
• Describe the physics by refining and quantifying the mental image of the problem.
• Plan a solution. This can be done by turning the concepts into math.
• Execute the plan using basic mathematical functions like algebra and calculus.
• Evaluate the answer. This can be done by asking yourself what a wrong answer would look like.