# Electric Charges and Fields Notes, Class 12 Physics | SwaVid

Electric Charges and Fields, NCERT Class 12 Physics: notes with key ideas, formulas, common mistakes and 3 quick checks with worked answers.

Canonical: https://www.swavid.com/cbse/class-12/physics/chapter/electric-charges-and-fields

Source: https://www.swavid.com/cbse/class-12/physics/chapter/electric-charges-and-fields

# Electric Charges and Fields

## Formulas and definitions

## Key ideas

## Common mistakes

## Quick checks

## Keep going

## Questions parents ask

## Class 12 Physics on SwaVid

### Electric charge and its properties

### Coulomb's law

### Electric field and field lines

### Electric dipole

### Electric flux and Gauss's law

### Applications of Gauss's law

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SwaVid › CBSE › Class 12 › Physics › Electric Charges and Fields

Notes written by SwaVid from the NCERT textbook.

Class 12 Physics, Chapter 1. Key ideas, formulas and common mistakes.

CBSE prints 16 marks for Units I-II together, not for this chapter alone.

Short answer. This chapter introduces static electric charges, their fundamental properties, Coulomb's law of electrostatic forces, and the concept of electric fields. Students learn to calculate electric fields and fluxes using field superposition and Gauss's law for symmetrical charge distributions.

Source: NCERT Physics Part I (Reprint 2026-27) , Chapter 1, Electric Charges and Fields

Charge is an intrinsic scalar property of matter, occurring as positive or negative. It is conserved, additive, and quantised as integral multiples of the elementary charge e.

The electrostatic force between two point charges acts along the line joining them and is directly proportional to the product of their charges and inversely proportional to the square of the distance between them. In vacuum, the constant of proportionality is 1 / (4πε₀).

An electric field is the force experienced per unit positive test charge placed at a point. Field lines originate on positive charges, terminate on negative charges, never cross each other, and do not form closed loops.

A pair of equal and opposite point charges separated by a small distance forms an electric dipole with dipole moment p directed from negative to positive. In a uniform field, a dipole experiences a torque τ = p × E but zero net translational force.

Electric flux measures the total field lines passing through a surface. Gauss's law states that the total outward flux through any closed surface equals the enclosed charge divided by ε₀.

Gauss's law simplifies electric field calculations for highly symmetric distributions, such as an infinitely long straight wire, an infinite plane sheet, and a thin spherical shell.

Try each question first. Then tap it to see the answer.

F = (1 / (4πε₀)) × (q₁ q₂ / r²)

F = (9.0 × 10⁹) × ((2.0 × 10⁻⁷) × (3.0 × 10⁻⁷)) / (0.30)²

F = (9.0 × 10⁹) × (6.0 × 10⁻¹⁴) / 0.09 = 6.0 × 10⁻³ N

6.0 × 10⁻³ N (repulsive)

p = q × 2a = (4.0 × 10⁻⁶ C) × (5.0 × 10⁻³ m) = 2.0 × 10⁻⁸ C m

τ = p E sin θ = (2.0 × 10⁻⁸) × (2.0 × 10⁵) × sin 30°

τ = (4.0 × 10⁻³) × 0.5 = 2.0 × 10⁻³ N m

2.0 × 10⁻³ N m

Φ = q / ε₀

Φ = (2.0 × 10⁻⁶ C) / (8.85 × 10⁻¹² C² N⁻¹ m⁻²)

Φ = 2.26 × 10⁵ N m² C⁻¹

2.26 × 10⁵ N m² C⁻¹

Electrostatic Potential and Capacitance .

Current Electricity .

Moving Charges and Magnetism .

The 14 chapters of Class 12 Physics .

CBSE does not give marks to one chapter. It prints 16 marks for Units I-II together (Electrostatics; Current Electricity). Electric Charges and Fields is part of that group.

No. They are written by SwaVid from the NCERT textbook. The CBSE curriculum is the reference for what is assessed.

Electrostatic Potential and Capacitance.

SwaVid is an AI tutor for Indian students in Classes 6 to 12. It finds the earlier ideas a child missed, then teaches today’s chapter. Start free to see how it works.

- Ch 1 NCERT book
- 16 marks, Units I-II together
- 3 quick checks
- Setting the electric dipole moment direction from positive to negative . By convention in physics, the electric dipole moment vector points from the negative charge (-q) to the positive charge (+q).
- Assuming the electric field of a dipole falls off as 1 / r² . The electric field of a single point charge falls off as 1 / r², but the dipole field falls off more rapidly as 1 / r³ at large distances.
- Assuming the electric field in Gauss's law is only due to enclosed charges . The electric field in Gauss's law is due to all charges, both inside and outside the surface, even though the net flux depends only on the enclosed charge.
- Thinking a uniform electric field exerts a net translational force on an electric dipole . In a uniform field, equal and opposite forces act on the two charges, giving zero net force; it only experiences a torque.

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