Class 12 Physics Notes: Chapter-wise Revision for CBSE Boards

These class 12 physics notes give a quick, chapter-wise revision of the full NCERT book. The CBSE syllabus has 14 chapters, and the paper has 70 marks for theory and 30 for practicals. Because physics rewards understanding more than memory, the notes below pair each chapter with its core ideas and formulas. First, check the marks distribution. Then revise the chapters in order, and finally use the common mistakes list before the exam.

Class 12 Physics Marks Distribution

The theory paper has five blocks of marks. Knowing this helps you plan your time.

Block	Chapters	Marks
Electrostatics and Current Electricity	1–3	16
Magnetism, EMI and AC	4–7	17
EM Waves and Optics	8–10	18
Dual Nature, Atoms and Nuclei	11–13	12
Electronic Devices	14	7

Practicals carry 30 marks, and they include two experiments (14), the record file (5), an activity (3), the project (3) and the viva (5). Therefore, steady lab work can add a safe 30 marks to your total.

Chapter 1: Electric Charges and Fields

Because charge is quantised and conserved, it always comes in whole multiples of e. Coulomb’s law gives the force between two point charges: F = k q₁q₂ / r², where k is about 9 × 10⁹ N m² C⁻². The electric field at a point is the force per unit test charge. Next, field lines show direction, and they never cross. Gauss’s law states that the total flux through a closed surface equals the enclosed charge divided by ε₀. As a result, you can find the field of a long wire, an infinite sheet and a charged shell with simple steps.

Chapter 2: Electrostatic Potential and Capacitance

Because potential falls with distance, V = kq / r at a distance r from a point charge. Work done in moving a charge depends only on the potential difference. An equipotential surface has the same potential everywhere, so no work is done along it. For capacitors, C = Q / V, and a parallel-plate capacitor has C = ε₀A / d. In series, 1/C adds up, but in parallel, the capacitances add. The energy stored is U = ½CV². Also, a dielectric increases the capacitance by the factor K.

Chapter 3: Current Electricity

Ohm’s law states V = IR for a conductor if the temperature stays constant. Resistivity depends on the material, so R = ρL / A. Drift velocity relates to current by I = nAev_d. Kirchhoff’s two laws solve complex circuits: the junction rule conserves charge, and the loop rule conserves energy. Meanwhile, a Wheatstone bridge stays balanced when P/Q = R/S. A cell with internal resistance r gives a terminal voltage V = E − Ir. Finally, the potentiometer compares emfs without drawing current.

Chapter 4: Moving Charges and Magnetism

A moving charge in a magnetic field feels the force F = q(v × B). Because the force is perpendicular to the velocity, the charge moves in a circle or a helix. The Biot–Savart law gives the field of a current element. At the centre of a circular loop, B = μ₀I / 2R. A long solenoid has B = μ₀nI inside it. Ampere’s circuital law makes such problems easy. Further, a current-carrying loop in a field feels the torque τ = NIAB sinθ, which is the principle of the moving-coil galvanometer.

Chapter 5: Magnetism and Matter

A bar magnet behaves as a magnetic dipole with moment m, so it always has two poles. Magnetic field lines form closed loops, so the net flux through a closed surface is zero. Earth’s field has three elements: declination, dip and horizontal component. Materials are diamagnetic, paramagnetic or ferromagnetic, depending on their response to a field. Therefore, learn the susceptibility signs and examples for each type.

Chapter 6: Electromagnetic Induction

Faraday’s law says the induced emf is e = −dΦ/dt. Lenz’s law gives the negative sign, because the induced current opposes the change that causes it. For a rod of length l moving with speed v in a field B, the motional emf is e = Blv. Self-inductance and mutual inductance measure how strongly circuits induce emf in themselves and in each other. The energy stored in an inductor is ½LI². Eddy currents also appear in solid conductors, and they are useful in induction furnaces.

Chapter 7: Alternating Current

For an AC source, the rms current is I₀ / √2. A resistor, an inductor and a capacitor behave differently: X_L = ωL and X_C = 1 / ωC. In a series LCR circuit, the impedance is Z = √(R² + (X_L − X_C)²). At resonance, X_L equals X_C, so the current peaks, and ω = 1 / √(LC). The power factor is cosφ. A transformer works on mutual induction, so V_s / V_p = N_s / N_p.

Chapter 8: Electromagnetic Waves

Maxwell added the displacement current to Ampere’s law, and this led to the idea of EM waves. These waves are transverse, and they travel at c = 1 / √(μ₀ε₀) in vacuum. The spectrum runs from radio waves through microwaves, infrared, visible light, ultraviolet and X-rays to gamma rays. Therefore, remember the order of increasing frequency, along with one use of each.

Chapter 9: Ray Optics and Optical Instruments

The mirror formula is 1/v + 1/u = 1/f, and the lens formula is 1/v − 1/u = 1/f. Refraction follows Snell’s law, n = sin i / sin r. Total internal reflection happens when light moves from a denser to a rarer medium beyond the critical angle. The lens maker’s formula links focal length with the radii and refractive index. For a prism, the deviation depends on the angle of incidence. Finally, the microscope and the telescope increase the visual angle, so learn their ray diagrams and magnifying powers.

Chapter 10: Wave Optics

Huygens’ principle explains reflection and refraction because it treats each point of a wavefront as a new source. In Young’s double-slit experiment, the fringe width is β = λD / d. Interference needs coherent sources, while diffraction shows the bending of waves at an obstacle. For a single slit, the central maximum is the widest. Polarisation proves that light is a transverse wave, and Brewster’s law gives tan i_B = n.

Chapter 11: Dual Nature of Radiation and Matter

Einstein’s photoelectric equation is K_max = hν − φ. Below the threshold frequency, no electrons are emitted, however intense the light. The stopping potential measures the maximum kinetic energy. Because light behaves as particles called photons, the wave theory cannot explain the effect. De Broglie proposed that matter also has a wave nature, with λ = h / p. The Davisson–Germer experiment supports this idea.

Chapter 12: Atoms

Rutherford’s alpha-scattering experiment showed a small, dense nucleus, so most of an atom is empty space. Bohr’s model fixed that atoms have stable orbits with quantised angular momentum. The energy of the nth level of hydrogen is E_n = −13.6 / n² eV. When an electron falls to a lower level, the atom emits a photon. Consequently, the Lyman, Balmer and Paschen series appear in the ultraviolet, visible and infrared regions.

Chapter 13: Nuclei

The nuclear radius follows R = R₀A^(1/3), so nuclear density is nearly constant. The mass defect gives the binding energy through E = Δm c². Because radioactive decay is random, it obeys N = N₀e^(−λt), and the half-life is T½ = 0.693 / λ. In fission, a heavy nucleus splits, and then it releases energy. In fusion, light nuclei join and also release energy, as in the Sun.

Chapter 14: Semiconductor Electronics

When a p-n junction forms, a depletion region appears, so current flows in one direction when it is forward biased. Diodes work as rectifiers, and the Zener diode regulates voltage. Also, LEDs, photodiodes and solar cells are optoelectronic devices. Finally, logic gates such as AND, OR, NOT, NAND and NOR need their truth tables and symbols.

Common Mistakes in Class 12 Physics Answers

• Students forget the units in numericals, so they lose a mark even when the value is right.
• Many draw ray diagrams without arrows or labels.
• Some mix up the formulas for lens and mirror, because the sign of u changes.
• Because signs matter in Lenz’s law and sign conventions, always state the direction clearly.
• When a derivation is asked, skip no step, since each step carries marks.

How to Revise Class 12 Physics Notes in 30 Days

Spend the first ten days on Electrostatics to AC, since these chapters have heavy numericals. Next, use the following ten days for optics and modern physics. Then give five days to semiconductors and practicals. Finally, solve sample papers in the last five days. For the chemistry side, read electrochemistry class 12 notes or the Class 11–12 Chemistry notes. You can also browse the Class 11–12 Physics notes, the full Class 11–12 notes hub, and how to stop procrastinating.

Wrap-Up

Class 12 physics notes work best as a revision tool after you have read each chapter once. Use the marks table to plan, practise diagrams and numericals, and revise formulas daily. Then continue with the Class 11–12 Physics category, or return to the The Note homepage.