Class 12 · Formulas

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NEET & JEE SPECIAL

Class 12 Physics Formulas

Continuous scrolling sheet of all essential Class 12 formulas required for NEET, JEE Main/Advanced, and board exams.

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Chapter 1

Electric Charges & Fields

Coulomb's lawF = kq1q2/r2
Field of point chargeE = kQ/r2
Dipole momentp = q(2a)
Torque on dipoleτ = p × E
Gauss's lawΦ = qenc/ε0

Chapter 2

Potential & Capacitance

Potential of point chargeV = kQ/r
CapacitanceC = Q/V
Parallel plateC = Kε0A/d
Energy storedU = ½CV2
Series1/C = Σ 1/Ci
ParallelC = ΣCi

Chapter 3

Current Electricity

Current & driftI = nAevd
Ohm's lawV = IR
ResistanceR = ρℓ/A
Terminal voltageV = ε − Ir
PowerP = VI = I2R = V2/R
Wheatstone balanceP/Q = R/S

Chapter 4

Moving Charges & Magnetism

Lorentz forceF = q(v × B)
Long straight wireB = μ0I/2πr
Centre of loopB = μ0I/2R
SolenoidB = μ0nI
Force on wireF = BIℓ sin θ
Radius in fieldr = mv/qB

Chapter 5

Magnetism & Matter

Dipole moment of loopm = NIA
Torqueτ = m × B
Gauss (magnetism)∮B·dA = 0
Susceptibilityχ = M/H
Relative permeabilityμr = 1 + χ

Chapter 6

Electromagnetic Induction

Faraday's lawε = −dΦ/dt
Motional emfε = Bℓv
Self-inductanceL = Φ/I,   ε = −L dI/dt
Energy in inductorU = ½LI2
Solenoid inductanceL = μ0n2Aℓ

Chapter 7

Alternating Current

RMS currentIrms = I0/√2
ReactancesXL = ωL,   XC = 1/ωC
ImpedanceZ = √(R2 + (XL − XC)2)
Resonanceω0 = 1/√(LC)
Average powerP = VrmsIrms cos φ
TransformerVs/Vp = Ns/Np

Chapter 8

Electromagnetic Waves

Speed of lightc = 1/√(μ0ε0)
Field ratioE0/B0 = c
Displacement currentId = ε0 dΦE/dt
IntensityI = ½ε0E02c

Chapter 9

Ray Optics

Mirror formula1/v + 1/u = 1/f
Lens formula1/v − 1/u = 1/f
Lens maker's1/f = (n − 1)(1/R1 − 1/R2)
Snell's lawn1 sin θ1 = n2 sin θ2
Critical anglesin C = 1/n
Power of lensP = 1/f (dioptre)

Chapter 10

Wave Optics

Fringe width (YDSE)β = λD/d
Single-slit minimaa sin θ = nλ
IntensityI = I0 cos2(φ/2)
Malus' lawI = I0 cos2θ
Brewster's lawtan ip = n

Chapter 11

Dual Nature

Photon energyE = hν = hc/λ
Photoelectric equationKmax = hν − φ
Stopping potentialeV0 = Kmax
de Broglieλ = h/p = h/√(2mK)
Electron through Vλ ≈ 12.27/√V Å

Chapter 12

Atoms

Orbit radiusrn = 0.529 n2/Z Å
Energy levelsEn = −13.6 Z2/n2 eV
Spectral lines1/λ = R(1/n12 − 1/n22)
Rydberg constantR = 1.097 × 107 m−1
Angular momentumL = nh/2π

Chapter 13

Nuclei

Nuclear radiusR = R0A1/3
Binding energyBE = Δm × 931.5 MeV
Decay lawN = N0e−λt
Half-lifeT½ = 0.693/λ
ActivityA = λN

Chapter 14

Semiconductor Electronics

Transistor currentsIE = IB + IC
Current gainsα = IC/IE,   β = IC/IB
Relationβ = α/(1 − α)
Intrinsic carriersne = nh = ni
Mass actionnenh = ni2
De Morgan(A·B)′ = A′ + B′

Most-confused formulas

The 6 Class 12 formulas students get wrong most often

Axial vs equatorial dipole field

Eaxial = 2kp/r3   Eeq = kp/r3

The axial field is exactly twice the equatorial one, and they point in opposite senses.

Capacitor: battery on or off?

V fixed ⇒ Q, U rise K×   Q fixed ⇒ V, U fall K×

Decide first whether the battery stays connected — every other step depends on it.

Field on the axis of a loop

B = μ0IR2 / [2(R2 + x2)3/2]

At the centre (x = 0) it reduces to μ0I/2R — not μ0I/2πR, which is the straight wire.

Impedance and power factor

Z = √(R2 + (XL − XC)2), cosφ = R/Z

Reactances subtract before squaring. Power uses cosφ, never the plain product V×I.

Lens maker vs lens formula

1/f = (n−1)(1/R1 − 1/R2)   1/v − 1/u = 1/f

Mirror uses 1/v + 1/u = 1/f. The sign of u is almost always negative — mark it first.

de Broglie through a potential

λ = h/√(2meV) ≈ 12.27/√V Å

The shortcut gives Ångström, not metres, and holds for electrons only.