NEET Electrostatics Complete Chapter Notes by PW

Understanding electric charge is the first step towards studying electrostatics. However, concepts such as electron transfer, charge quantisation, specific charge and the effects of charge motion can be confusing when you first encounter them.

PW online lectures introduce these fundamentals, explaining how bodies become charged and how electric charge behaves. Use the notes to revise the key concepts and prepare for questions based on the properties of charge.

Meaning of Electrostatics

Electrostatics is the study of electric charges at rest and the effects produced by them.

A property is a characteristic of a body because of which it produces or experiences a particular effect. For example, mass is associated with gravitational effects, while electric charge is responsible for electromagnetic interactions.

Electric Charge as a Property of Matter

Electric charge is a property of matter because of which a body experiences or produces electromagnetic forces.

Mass is associated with gravitational force, while electric charge is associated with electromagnetic force. The gravitational force between two masses is given by:

F = Gm₁m₂ / r²

Here, G is the universal gravitational constant, m₁ and m₂ are the masses, and r is the distance between them.

Charges of Fundamental Particles

The charge of an electron is:

qₑ = -e = -1.6 × 10⁻¹⁹ C

The charge of a proton is:

qₚ = +e = +1.6 × 10⁻¹⁹ C

The charge of a neutron is:

qₙ = 0

An electron carries a negative charge, a proton carries a positive charge, and a neutron is electrically neutral.

Charge on Multiple Particles

• Ten electrons: q = -10e = -1.6 × 10⁻¹⁸ C

• One deuteron, containing one proton and one neutron: q = +e

• One alpha particle, containing two protons and two neutrons: q = +2e = +3.2 × 10⁻¹⁹ C

The electron is an elementary particle, whereas a proton consists of quarks.

Charging of a Body

An atom contains protons and neutrons in its nucleus, with electrons around the nucleus. An atom is electrically neutral when its total positive and negative charges cancel.

For an atom containing four protons, four neutrons and four electrons:

Q = +4e + 0 - 4e = 0

Positive Charging

A body becomes positively charged when electrons are removed from it. This creates a deficiency of electrons.

If one electron is removed from the neutral atom containing four protons and four electrons:

Q = +4e - 3e = +e

If two electrons are removed:

Q = +4e - 2e = +2e

The body's mass decreases slightly because electrons have been removed.

Negative Charging

A body becomes negatively charged when electrons are added to it. This creates an excess of electrons.

If two electrons are added to the same neutral atom:

Q = +4e - 6e = -2e

The body's mass increases slightly because it gains electrons.

Remember: Positive charging involves electron removal, while negative charging involves electron addition. Ordinary charging occurs through electron transfer, not proton transfer. Protons are bound inside the nucleus, and transferring them requires a nuclear process.

Types and Properties of Charge

There are two types of electric charge:

• Positive charge

• Negative charge

A neutral body has zero net charge, but neutrality is not a third type of charge.

A charged body has mass and a non-zero net charge. A neutral body also has mass, even though its net charge is zero.

Units of Charge

The SI unit of electric charge is the coulomb (C).

Important unit conversions include:

• 1 C = 3 × 10⁹ statcoulombs (ESU)

• 1 C = 0.1 emu of charge

• 1 Faraday ≈ 96,500 C

ESU, statcoulomb and Franklin refer to the same CGS electrostatic unit of charge.

Dimension of Charge

Electric current is the rate of flow of charge:

I = Q / t

Therefore:

Q = It

The dimensional formula of charge is:

[Q] = [I][T] = [AT]

Here, I represents electric current and T represents time.

Charge as a Scalar Quantity

Electric charge is a scalar quantity. It has magnitude and sign but no direction. Charges are added algebraically, taking their signs into account.

For example:

(+4 C) + (+2 C) + (-3 C) = +3 C

Unlike forces, charges do not require vector addition.

Interaction Between Charges

• Like charges repel each other.

• Unlike charges attract each other.

Therefore, two positive charges repel, two negative charges repel, and a positive and a negative charge attract.

Attraction alone does not prove that a body is charged because a charged body can attract a neutral body through charge redistribution. Repulsion between suitably tested bodies is a more reliable indication of like charges.

Invariance of Charge

The charge of a body remains unchanged under rotation or translational motion, provided no charge is transferred to or from it.

Charge changes when electrons are transferred. Simply rotating or moving a body does not change its net charge.

Specific Charge

Specific charge is the ratio of the charge of a particle to its mass.

Specific charge = q / m

For a proton:

q / m = e / mₚ

For a deuteron, whose mass is approximately twice the proton mass:

q / m ≈ e / (2mₚ)

For an alpha particle, whose charge is +2e and mass is approximately 4mₚ:

q / m ≈ 2e / 4mₚ = e / (2mₚ)

Thus, the specific charge of a deuteron and an alpha particle is approximately the same.

For a charged particle moving at relativistic speeds, its charge remains constant while its relativistic energy and momentum increase. The decrease in charge-to-mass ratio is sometimes described using relativistic mass; in modern treatments, the particle's invariant rest mass remains constant.

Charge Motion and Electromagnetic Effects

The effects associated with a charge depend on its state of motion.

• Charge at rest: Produces an electric field.

• Charge moving with constant velocity: Produces electric and magnetic fields.

• Accelerating charge: Produces electric and magnetic fields and can emit electromagnetic radiation.

Remember the sequence: rest produces an electric field; constant motion produces electric and magnetic fields; acceleration can produce electromagnetic radiation.

Quantisation of Charge

Electric charge is quantised, meaning the net charge on an ordinary isolated body is an integral multiple of the elementary charge.

q = ne

Here, n is an integer and e = 1.6 × 10⁻¹⁹ C.

Possible net charges include:

±e, ±2e, ±3e, ...

For ordinary bodies charged through electron transfer, fractional values such as 1.5e are not possible because electrons are transferred in whole numbers. Quarks have fractional elementary charges, but they are not observed as isolated particles under ordinary conditions.

Watch 1st FREE Physics Class: Lakshya NEET 2027 One Shot Video by PW to revise electrostatics, charging of a body, types and properties of charge, and quantisation of charge. Follow the lecture timestamps to revisit specific concepts and strengthen your understanding of the fundamentals.

Electrostatics begins with understanding electric charge, how a body becomes charged and the properties that distinguish charge from other physical quantities. Revise electron transfer, charge quantisation, scalar addition, specific charge and the effects of charge motion to build a strong foundation for further electrostatics topics.

NEET Resources You Might Like: