NCERT Notes Class 12 Physics Chapter 1 Electric Charges and Fields

Class 12 Physics Chapter 1 Electric Charges and Fields opens the electrostatics block. The chapter introduces Coulomb's law, the electric field, the electric dipole, and Gauss's law. It carries 6 marks in CBSE and 4 to 5 percent in JEE Main. This page hosts the class 12 physics chapter 1 notes PDF and the NCERT chapter 1 physics class 12 notes reference.

• CBSE Boards: 6 marks, usually one 5-mark Gauss's-law derivation plus one 1-mark on Coulomb's law.
• JEE Main: 4 to 5 percent, two questions per shift on Coulomb's law, dipole, and Gauss applications.
• NEET: 1 to 2 questions every year on point-charge field and dipole concepts.

Each entry in these chapter 1 physics class 12 notes is curated by Collegedunia subject experts, mapped to the 2026-27 NCERT, and refined against the last five years of CBSE Board, JEE Main, and NEET papers.

You can find the complete electric charges and fields class 12 notes pdf, including Coulomb's law, electric field, electric dipole, Gauss's law applications (infinite wire, plane sheet, spherical shell), and continuous charge distributions, in the article below. The class 12 ch 1 physics notes also cover the JEE Main extensions on dipole torque and charged-ring axial field.

Also Check:

• Class 12 Electric Charges and Fields NCERT Solutions
• Class 12 Physics Chapter 1 Formula Sheet

Why Physics Class 12 Chapter 1 Is the Foundation of All Electrostatics

• Fundamental concepts reused across all four electrostatics chapters.
• Skipping this chapter makes every later chapter harder than necessary.
• Coverage: all 5 sub-topics + JEE Main extensions (force on dipole in non-uniform field, electric quadrupole, charged ring axis).

Electric Charges and Fields Notes Video Walkthrough

Source: Magnet Brains on YouTube

Topic-by-Topic Concept Summary for Class 12 Ch 1 Physics

The chapter splits into five sub-topic blocks. The walkthrough below maps each block to its CBSE marking pattern.

• Electric charge and its properties: 1-mark MCQ on quantisation (q = n e), conservation of charge, additivity.
• Coulomb's law and superposition principle: 3-mark numerical on the vector form F = k q_1 q_2 (r_hat) / r squared, plus superposition for multiple charges.
• Electric field, field lines, and dipole: 3 to 5-mark derivation block. The electric field of a dipole on its axial and equatorial lines is the most-asked 5-marker in JEE Main from class 12 chapter 1 physics.
• Electric flux and Gauss's law: 5-mark derivation block. Three classic applications: infinite line charge, infinite plane sheet, uniformly charged spherical shell.
• Continuous charge distributions: 3-mark conceptual on linear (lambda), surface (sigma), and volume (rho) charge densities.

Coulomb's Law and the Vector Form

Coulomb's law: the electrostatic force between two point charges is proportional to the product of charges and inversely proportional to the square of the distance. Vector form: F_12 = k (q_1 q_2 / r squared) r_hat_12, where r_hat_12 is the unit vector from charge 2 to charge 1, and k = 9 times 10^9 N m squared / C squared in vacuum.

Three facts to remember:

• Coulomb's law applies to point charges only (or sources much smaller than the separation).
• Sign convention: like charges repel, unlike charges attract. The sign of the product q_1 q_2 sets the direction.
• Superposition: total force on a charge is the vector sum of forces from each source charge.

Electric Field of an Electric Dipole: Axial and Equatorial

An electric dipole = two equal and opposite charges separated by 2a. Dipole moment p = q (2a), pointing from negative to positive, SI unit C m. The dipole field has two standard cases:

• Axial line (along the dipole axis): E_axial = 2 k p / r cubed, directed along p (for r >> a).
• Equatorial line (perpendicular bisector): E_equatorial = k p / r cubed, directed opposite to p (for r >> a).

The ratio E_axial / E_equatorial = 2 at the same distance. The 1/r cubed dependence (versus 1/r squared for a point charge) is the signature of a dipole field: the most-asked 1-mark MCQ from physics class 12 electric charges and fields.

Torque on a dipole in a uniform field: tau = p cross E, magnitude p E sin theta. Potential energy: U = minus p . E = minus p E cos theta.

Gauss's Law and Its Three Standard Applications

Gauss's law: the total electric flux through any closed surface = enclosed charge / epsilon_0. closed-integral of E . dA = Q_enclosed / epsilon_0. The Gaussian surface is a mathematical construct, chosen to exploit the symmetry of the charge distribution.

Three classic applications:

• Infinite straight line of charge (linear density lambda): Gaussian surface = cylinder. E = lambda / (2 pi epsilon_0 r), directed radially outward.
• Infinite plane sheet (surface density sigma): Gaussian surface = pillbox. E = sigma / (2 epsilon_0), constant and perpendicular. For a conducting sheet: E = sigma / epsilon_0.
• Uniformly charged spherical shell: Gaussian surface = concentric sphere. Outside: E = k Q / r squared. Inside: E = 0.

The single most-asked 5-marker from this chapter is one of these three derivations. The physics class 12 chapter 1 pdf and the class 12 physics chapter 1 notes PDF on this page includes the labelled diagram CBSE markers expect.

Electric Field Lines: Five Properties Boards Test

Field lines visualise the electric field direction. Five properties recur in CBSE 2-mark questions:

1. Tangent to a field line gives the direction of E at that point.
2. Lines start from positive charges and terminate on negative charges.
3. Lines never intersect (intersection would imply two field directions at a point).
4. Density of lines = field magnitude (denser lines = stronger field).
5. Lines do not form closed loops in electrostatics (E is a conservative field).

Continuous Charge Distributions: Densities

When charge is spread continuously:

• Linear charge density lambda (C/m): wires, rods, rings.
• Surface charge density sigma (C/m²): plates, sheets, conductors.
• Volume charge density rho (C/m³): spherical clouds, charged balls.

Total charge: Q = ∫ lambda dl (line), ∫ sigma dA (surface), ∫ rho dV (volume). Electric field at a point is the integral of dE over the distribution.

Class 12 Physics Chapter 1 All Formulas: Quick-Reference Table

The class 12 physics chapter 1 all formulas list below covers every numerical in the chapter. The same table sits on the back of the physics class 12 chapter 1 pdf for last-minute revision.

Full formula sheet with derivations: Class 12 Physics Chapter 1 Formula Sheet

Class 12 Physics Chapter 1 All Derivations: Index Table

Seven derivations carry the bulk of the marks across the class 12 physics chapter 1 all derivations set. Each derivation in the chapter 1 physics class 12 notes PDF carries the full geometry sketch, the integral set-up, and the boundary-condition substitution.

Electric Charges and Fields Weightage Compared Across Class 12 Physics Chapters

The table below maps how Class 12 Physics Chapter 1 weightage compares with every other chapter. Marks are CBSE board averages over the last five papers.

Electric Charges and Fields Previous Year Questions Weightage (2021 to 2026)

The table below maps every CBSE Board, JEE Main, and NEET appearance of Class 12 Physics Chapter 1 topics over the last six sessions.

Common Mistakes in Class 12 Chapter 1 Physics

Student Pulse: Chapter 1 Difficulty Rating from Our Student Poll

In a Collegedunia poll of 13,150 Class 12 Physics students conducted before the 2026 boards, 71% of students rated the dipole equatorial derivation as the trickiest sub-topic, ahead of the Gauss's law applications.

Solved Example: Electric Field at the Centre of a Charged Ring

Problem. A thin ring of radius R = 10 cm carries Q = 5 microcoulombs uniformly. Find E at the centre and at an axial point 20 cm from the centre.

Step 1. At the centre: each element dq has a symmetric partner; fields cancel. E = 0.

Step 2. At an axial point distance x: only the axial component survives. E = k Q x / (R squared + x squared)^(3/2).

Step 3. Substituting x = 0.20 m, R = 0.10 m: (R² + x²) = 0.05, (0.05)^(3/2) ≈ 0.01118. E = (9×10⁹ × 5×10⁻⁶ × 0.20) / 0.01118 ≈ 8.05 × 10⁵ N/C.

How to Revise in 90 Minutes

• 0 to 25 min: Coulomb's law + vector form + superposition. Solve 2 numericals.
• 25 to 50 min: Dipole axial and equatorial fields + torque + potential energy.
• 50 to 75 min: Gauss's law derivations (wire, sheet, shell). Sketch each Gaussian surface.
• 75 to 90 min: Continuous charge distributions + flush through the 14-formula reference.

Budget 5 to 6 hours for first-read if you're new to electrostatics. The chapter 1 physics class 12 notes are best read after Class 11 mechanics (work and energy).

More Class 12 Electric Charges and Fields Resources

NCERT Notes for Class 12 Physics: All Chapters