Class 12 Physics
The formulae, and nothing else
Electrostatics
- Coulomb's law
- F = (1/4πε₀) · q₁q₂/r²
- Electric field
- E = F/q₀ = (1/4πε₀) · q/r²
- Dipole moment
- p = q · 2a
- Torque on dipole
- τ = p × E
- Gauss's law
- ∮ E·dA = q_enc/ε₀
- Potential
- V = (1/4πε₀) · q/r
- Capacitance (parallel plate)
- C = ε₀A/d
- Energy in a capacitor
- U = ½CV² = ½QV = Q²/2C
- Capacitors in series
- 1/C = 1/C₁ + 1/C₂ + …
- Capacitors in parallel
- C = C₁ + C₂ + …
Current electricity
- Drift velocity
- v_d = eEτ/m, I = neAv_d
- Resistivity
- R = ρL/A
- Conductivity
- σ = 1/ρ = ne²τ/m
- Kirchhoff's rules
- Σ I = 0 at a junction · Σ V = 0 round a loop
- Wheatstone balance
- P/Q = R/S
- Cells in series
- ε = ε₁ + ε₂, r = r₁ + r₂
Magnetism & induction
- Biot–Savart
- dB = (μ₀/4π) · I dl sinθ / r²
- Field, straight wire
- B = μ₀I / 2πr
- Field, solenoid centre
- B = μ₀nI
- Force on a conductor
- F = BIL sinθ
- Torque on a loop
- τ = NBIA sinθ
- Faraday's law
- ε = −N dΦ/dt
- Self inductance
- ε = −L dI/dt
- Transformer
- V_s/V_p = N_s/N_p = I_p/I_s
- Resonance (LCR)
- f = 1 / 2π√(LC)
Optics
- Mirror formula
- 1/v + 1/u = 1/f, f = R/2
- Lens formula
- 1/v − 1/u = 1/f
- Magnification
- m = v/u (lens) · m = −v/u (mirror)
- Lens maker
- 1/f = (n−1)(1/R₁ − 1/R₂)
- Power
- P = 1/f (metres), dioptres
- Refractive index
- n = c/v = sin i / sin r
- Critical angle
- sin C = 1/n
- Young's fringe width
- β = λD/d
- Compound microscope
- M = (L/f_o)(D/f_e)
- Telescope
- M = f_o/f_e
Modern physics
- Photoelectric
- hν = φ₀ + ½mv²_max
- Stopping potential
- eV₀ = hν − φ₀
- de Broglie
- λ = h/p = h/mv
- Bohr radius
- r_n = 0.529 n²/Z Å
- Bohr energy
- E_n = −13.6 Z²/n² eV
- Mass–energy
- E = mc²
- Radioactive decay
- N = N₀e^(−λt), t½ = 0.693/λ
Electronic devices
- Diode, forward bias
- Low resistance, current flows
- Half-wave rectifier
- Output for one half cycle · ripple 1.21
- Full-wave rectifier
- Output for both halves · ripple 0.48
- Energy gap
- Conductor ≈ 0 · Semiconductor ≈ 1 eV · Insulator > 3 eV
Standard CBSE Class 12 Physics formulae. Check anything you are unsure of against NCERT before you rely on it — this is a memory aid, not a source.