In short: Class 12 Physics has 14 chapters and over 160 formulas covering Electrostatics, Current Electricity, Magnetism, Optics, and Modern Physics. This chapter-wise formula sheet lists every important equation with SI units for the 2027 CBSE board exam. Essential for board revision, JEE, and NEET preparation.
Why Class 12 Physics Formulas Are Board Exam Gold
Class 12 Physics carries 70 marks in the CBSE board exam. Roughly 40-50% of the paper involves direct numerical problems where you apply a formula, substitute values, and calculate. Another 20-30% involves derivations that start from these formulas.
If you know every formula, its unit, and when to apply it, you can score 50+ marks on formula-based questions alone. This sheet gives you exactly that - every chapter's formulas in one place.
This follows the CBSE 2026-27 syllabus structure. Let us go chapter by chapter.
Chapter 1 - Electric Charges and Fields
| Formula | Expression | Unit |
|---|---|---|
| Coulomb's law | F = kq1q2/r^2, where k = 9 x 10^9 N m^2/C^2 | N |
| Electric field | E = F/q = kQ/r^2 | N/C or V/m |
| Electric field (dipole, axial) | E = 2kp/r^3 (for r >> a) | N/C |
| Electric field (dipole, equatorial) | E = kp/r^3 (for r >> a) | N/C |
| Electric dipole moment | p = q x 2a | C m |
| Torque on dipole | tau = pE sin(theta) | N m |
| Electric flux | phi = E . A = EA cos(theta) | N m^2/C or V m |
| Gauss's law | phi = q(enclosed) / epsilon(0) | N m^2/C |
| epsilon(0) | 8.854 x 10^-12 C^2/(N m^2) | - |
Chapter 2 - Electrostatic Potential and Capacitance
| Formula | Expression | Unit |
|---|---|---|
| Electric potential | V = kQ/r | V (Volt) |
| Potential energy | U = kq1q2/r | J |
| Potential (dipole, axial) | V = kp cos(theta)/r^2 | V |
| Relation E and V | E = -dV/dr | V/m |
| Capacitance | C = Q/V | F (Farad) |
| Parallel plate capacitor | C = epsilon(0) A / d | F |
| With dielectric | C = K epsilon(0) A / d | F |
| Energy stored | U = (1/2)CV^2 = (1/2)QV = Q^2/(2C) | J |
| Capacitors in series | 1/C(eq) = 1/C1 + 1/C2 + 1/C3 + ... | F |
| Capacitors in parallel | C(eq) = C1 + C2 + C3 + ... | F |
Chapter 3 - Current Electricity
| Formula | Expression | Unit |
|---|---|---|
| Current | I = Q/t = neAv(d) | A (Ampere) |
| Ohm's law | V = IR | V |
| Resistance | R = rho L / A | Ohm |
| Resistivity | rho = m / (ne^2 tau) | Ohm m |
| Drift velocity | v(d) = eE tau / m = I/(neA) | m/s |
| Resistors in series | R(eq) = R1 + R2 + R3 + ... | Ohm |
| Resistors in parallel | 1/R(eq) = 1/R1 + 1/R2 + 1/R3 + ... | Ohm |
| Power | P = VI = I^2 R = V^2/R | W |
| EMF | E = V + Ir (internal resistance) | V |
| Kirchhoff's junction rule | Sum of currents at junction = 0 | - |
| Kirchhoff's loop rule | Sum of potential changes in closed loop = 0 | - |
| Wheatstone bridge | P/Q = R/S (balanced condition) | - |
| Meter bridge | R = S(100-l)/l | Ohm |
| Potentiometer | E1/E2 = l1/l2 | - |
| Temperature coefficient | R(T) = R(0)(1 + alpha T) | Ohm |
Chapter 4 - Moving Charges and Magnetism
| Formula | Expression | Unit |
|---|---|---|
| Lorentz force | F = q(v x B) = qvB sin(theta) | N |
| Force on current-carrying conductor | F = BIl sin(theta) | N |
| Biot-Savart law | dB = (mu0/4pi) I dl sin(theta) / r^2 | T |
| Magnetic field (straight wire) | B = mu0 I / (2 pi r) | T |
| Magnetic field (centre of circular loop) | B = mu0 I / (2R) | T |
| Ampere's circuital law | Integral B . dl = mu0 I(enclosed) | T m |
| Magnetic field (solenoid) | B = mu0 n I | T |
| Magnetic field (toroid) | B = mu0 n I | T |
| Radius of circular path | r = mv / (qB) | m |
| Cyclotron frequency | f = qB / (2 pi m) | Hz |
| mu0 | 4 pi x 10^-7 T m/A | - |
Chapter 5 - Magnetism and Matter
| Formula | Expression | Unit |
|---|---|---|
| Magnetic moment (bar magnet) | M = m x 2l | A m^2 |
| Torque on magnetic dipole | tau = MB sin(theta) | N m |
| Axial field (bar magnet) | B = (mu0/4pi) 2M/r^3 | T |
| Equatorial field (bar magnet) | B = (mu0/4pi) M/r^3 | T |
| Magnetic susceptibility | chi = M(intensity) / H | Dimensionless |
| Magnetic permeability | mu = mu0 (1 + chi) | T m/A |
| Curie's law | chi = C/T (paramagnetic) | - |
Chapter 6 - Electromagnetic Induction
| Formula | Expression | Unit |
|---|---|---|
| Magnetic flux | phi = BA cos(theta) | Wb (Weber) |
| Faraday's law | EMF = -d(phi)/dt | V |
| EMF (N turns) | EMF = -N d(phi)/dt | V |
| Motional EMF | EMF = Blv | V |
| Self-inductance | EMF = -L dI/dt | V |
| Inductance of solenoid | L = mu0 n^2 A l | H (Henry) |
| Mutual inductance | EMF = -M dI/dt | V |
| Energy in inductor | U = (1/2) L I^2 | J |
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Chapter 7 - Alternating Current
| Formula | Expression | Unit |
|---|---|---|
| AC voltage | V = V0 sin(omega t) | V |
| RMS voltage | V(rms) = V0 / sqrt(2) | V |
| RMS current | I(rms) = I0 / sqrt(2) | A |
| Impedance (LCR series) | Z = sqrt(R^2 + (XL - XC)^2) | Ohm |
| Inductive reactance | XL = omega L = 2 pi f L | Ohm |
| Capacitive reactance | XC = 1/(omega C) = 1/(2 pi f C) | Ohm |
| Resonant frequency | f(0) = 1 / (2 pi sqrt(LC)) | Hz |
| Power factor | cos(phi) = R/Z | Dimensionless |
| Average power | P = V(rms) I(rms) cos(phi) | W |
| Transformer ratio | V(s)/V(p) = N(s)/N(p) = I(p)/I(s) | - |
| Quality factor | Q = omega(0) L / R = 1/(omega(0) CR) | Dimensionless |
Chapter 8 - Electromagnetic Waves
| Formula | Expression | Unit |
|---|---|---|
| Speed of EM waves | c = 1/sqrt(mu0 epsilon0) = 3 x 10^8 m/s | m/s |
| Relation | c = f lambda | m/s |
| Energy density (electric) | u(E) = (1/2) epsilon0 E^2 | J/m^3 |
| Energy density (magnetic) | u(B) = B^2 / (2 mu0) | J/m^3 |
| Relation E and B | E = cB | - |
EM Spectrum (increasing frequency): Radio > Microwave > Infrared > Visible > Ultraviolet > X-rays > Gamma rays
Chapter 9 - Ray Optics
| Formula | Expression | Unit |
|---|---|---|
| Mirror formula | 1/v + 1/u = 1/f | m^-1 |
| Magnification (mirror) | m = -v/u = h(i)/h(o) | Dimensionless |
| Lens formula | 1/v - 1/u = 1/f | m^-1 |
| Magnification (lens) | m = v/u = h(i)/h(o) | Dimensionless |
| Lens maker's formula | 1/f = (mu - 1)(1/R1 - 1/R2) | m^-1 |
| Power of lens | P = 1/f (f in metres) | D (Dioptre) |
| Combination of lenses | P = P1 + P2 + ... | D |
| Snell's law | n1 sin(i) = n2 sin(r) | - |
| Critical angle | sin(C) = n2/n1 (n1 > n2) | Degrees |
| Prism deviation | delta = (i + e) - A | Degrees |
| Minimum deviation | mu = sin((A + D(m))/2) / sin(A/2) | - |
| Magnifying power (simple microscope) | m = 1 + D/f | Dimensionless |
| Magnifying power (compound microscope) | m = -(L/f(o))(D/f(e)) | Dimensionless |
| Magnifying power (telescope) | m = f(o)/f(e) | Dimensionless |
Chapter 10 - Wave Optics
| Formula | Expression | Unit |
|---|---|---|
| Path difference (constructive) | Delta = n lambda (n = 0,1,2,...) | m |
| Path difference (destructive) | Delta = (2n+1) lambda/2 | m |
| Young's double slit fringe width | beta = lambda D / d | m |
| Position of nth bright fringe | y(n) = n lambda D / d | m |
| Single slit first minimum | a sin(theta) = lambda | - |
| Brewster's angle | tan(i(p)) = n2/n1 | - |
| Malus's law | I = I0 cos^2(theta) | W/m^2 |
Chapter 11 - Dual Nature of Radiation and Matter
| Formula | Expression | Unit |
|---|---|---|
| Photoelectric equation | KE(max) = hf - phi = h(f - f0) | J |
| Threshold frequency | f0 = phi / h | Hz |
| Stopping potential | eV0 = hf - phi | J |
| de Broglie wavelength | lambda = h / (mv) = h / p | m |
| de Broglie (kinetic energy) | lambda = h / sqrt(2mKE) | m |
| de Broglie (accelerated electron) | lambda = 1.227 / sqrt(V) nm | nm |
Chapter 12 - Atoms
| Formula | Expression | Unit |
|---|---|---|
| Bohr radius | r(n) = 0.529 n^2 / Z angstrom | angstrom |
| Energy of nth orbit | E(n) = -13.6 Z^2 / n^2 eV | eV |
| Velocity | v(n) = 2.18 x 10^6 Z / n m/s | m/s |
| Wavelength of emitted photon | 1/lambda = RZ^2 (1/n1^2 - 1/n2^2) | m^-1 |
| Rydberg constant | R = 1.097 x 10^7 m^-1 | m^-1 |
Chapter 13 - Nuclei
| Formula | Expression | Unit |
|---|---|---|
| Nuclear radius | R = R0 A^(1/3), R0 = 1.2 x 10^-15 m | m |
| Mass defect | Delta m = [Zm(p) + (A-Z)m(n)] - M(nucleus) | u |
| Binding energy | BE = Delta m x 931.5 MeV | MeV |
| Binding energy per nucleon | BE/A | MeV/nucleon |
| Radioactive decay | N = N0 e^(-lambda t) | - |
| Half-life | T(1/2) = 0.693 / lambda | s |
| Mean life | tau = 1/lambda = T(1/2)/0.693 | s |
| Activity | A = lambda N = A0 e^(-lambda t) | Bq (disintegrations/s) |
Chapter 14 - Semiconductor Electronics
| Formula | Expression | Unit |
|---|---|---|
| Intrinsic semiconductor | n(e) = n(h) = n(i) | - |
| Mass action law | n(e) x n(h) = n(i)^2 | - |
| Current gain (CE) | beta = I(C) / I(B) | Dimensionless |
| Current gain (CB) | alpha = I(C) / I(E) | Dimensionless |
| Relation alpha and beta | beta = alpha / (1 - alpha) | - |
| Voltage gain | A(v) = beta x R(L) / R(in) | Dimensionless |
Logic gates truth table essentials:
| Gate | Output |
|---|---|
| AND | 1 only when both inputs are 1 |
| OR | 1 when any input is 1 |
| NOT | Inverts input |
| NAND | 0 only when both inputs are 1 |
| NOR | 1 only when both inputs are 0 |
How to Memorise 160+ Class 12 Physics Formulas
1. Build formula chains. Electrostatics and Current Electricity are connected. Coulomb's law leads to electric field, which leads to potential, which leads to capacitance. When you see the chain, you remember the sequence.
2. Compare analogies. Electrostatics and Magnetism have parallel formulas. Coulomb's law (F = kq1q2/r^2) mirrors the Biot-Savart concept. Gauss's law for electricity parallels Ampere's law for magnetism. Learn them in pairs.
3. Solve board-level numericals. CBSE asks 3-5 mark numerical problems. Each one requires 1-2 formulas. After solving 20 numericals per chapter, the formulas become automatic.
4. Use the unit check. If your answer has wrong units, your formula is wrong. Always write units alongside your calculation. This catches errors before the examiner does.
5. Revise with Padhaao. Tell the AI tutor which chapter you are revising. It generates targeted numerical problems and catches formula errors instantly. Much faster than checking an answer key.
Common Mistakes in Class 12 Physics
- Sign convention in optics. Concave mirror: f is negative. Convex lens: f is positive. Mixing these up gives wrong v and wrong magnification. Always state your sign convention before solving.
- Forgetting to convert units. Capacitance is often in microfarads, resistance in kilohms. If you do not convert to SI before substituting, your answer will be off by factors of 10^3 or 10^6.
- Using wrong formula for magnetic field. B = mu0 I/(2 pi r) is for a straight wire. B = mu0 I/(2R) is for the centre of a loop. B = mu0 nI is for a solenoid. Identify the geometry before picking the formula.
- Half-life vs mean life. T(1/2) = 0.693/lambda. Mean life = 1/lambda. These are not the same. Many students swap them in radioactivity problems.
- Phase difference in AC. In a pure inductor, current lags voltage by 90 degrees. In a pure capacitor, current leads voltage by 90 degrees. Getting this backwards ruins phasor diagrams.
Exam-Day Quick Revision Strategy
Minutes 1-10: Electrostatics and Current Electricity formulas. These chapters carry the most marks. Focus on Coulomb's law, capacitance, Ohm's law, Kirchhoff's laws, and Wheatstone bridge.
Minutes 11-20: Magnetism and EMI. Biot-Savart law, Faraday's law, self/mutual inductance, and AC impedance formula.
Minutes 21-30: Optics (mirror formula, lens formula, Snell's law, Young's double slit). These are high-scoring numerical topics.
Minutes 31-40: Modern Physics - photoelectric equation, de Broglie wavelength, Bohr model, radioactive decay, half-life.
Minutes 41-45: Quick scan of semiconductor formulas and logic gates. Take 5 deep breaths and go.
FAQ
How many formulas are in Class 12 Physics?
About 160-170 formulas across 14 chapters. Electrostatics, Current Electricity, and Optics contribute the most. Many formulas in Modern Physics are short and easy to remember.
Which chapters are most important for the board exam?
Electrostatics, Current Electricity, Ray Optics, and Wave Optics together carry about 50-55% of the total marks. Master these four chapters first.
Are Class 12 Physics formulas enough for JEE Main?
The formulas are the same, but JEE problems require applying them in more complex situations. You need to practise multi-concept problems where two or three formulas combine in one question.
Should I memorise derivations?
Yes. CBSE asks 3-5 mark derivation questions every year. Key derivations include Coulomb's law using Gauss's theorem, expression for capacitance, Biot-Savart law application, lens maker's formula, and de Broglie wavelength.
What is the fastest way to revise all formulas before the exam?
Use this formula sheet. Read each table, cover the expression column, and try to recall it. Mark what you cannot recall. Then focus only on the marked formulas. This takes 40-50 minutes and is the most efficient revision method.
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