Complete Class 12 Physics Formulas
Comprehensive reference with examples, calculators, and board-specific content for CBSE, ICSE & State Boards. Essential for JEE, NEET preparation.
Physics Topics
Electrostatics
Variables:
- F Force (N)
- k Coulomb’s Constant (9×10⁹ N·m²/C²)
- q₁, q₂ Charges (C)
- r Distance (m)
Example
Two charges of 2μC and 3μC are 0.1 m apart. Force between them is:
F = (9×10⁹ × 2×10⁻⁶ × 3×10⁻⁶) / (0.1)² = 5.4 N
Calculate Force
Variables:
- E Electric Field (N/C)
- k Coulomb’s Constant
- Q Source Charge (C)
- r Distance (m)
Example
Electric field at 0.2 m from 5μC charge:
E = (9×10⁹ × 5×10⁻⁶) / (0.2)² = 1.125×10⁶ N/C
Calculate Electric Field
Variables:
- V Electric Potential (V)
- k Coulomb’s Constant
- Q Charge (C)
- r Distance (m)
Example
Potential at 0.1 m from 2μC charge:
V = (9×10⁹ × 2×10⁻⁶) / 0.1 = 1.8×10⁵ V
Calculate Potential
Variables:
- C Capacitance (F)
- Q Charge (C)
- V Potential (V)
Example
A capacitor stores 10μC charge at 100V. Its capacitance is:
C = 10×10⁻⁶ / 100 = 0.1μF
Calculate Capacitance
Current Electricity
Variables:
- V Voltage (V)
- I Current (A)
- R Resistance (Ω)
Example
If 2A current flows through 10Ω resistor, voltage is:
V = 2 × 10 = 20V
Calculate Voltage
Variables:
- R Resistance (Ω)
- ρ Resistivity (Ω·m)
- L Length (m)
- A Area (m²)
Example
A copper wire (ρ=1.7×10⁻⁸ Ω·m) of length 10m and area 1mm² has resistance:
R = (1.7×10⁻⁸ × 10) / (1×10⁻⁶) = 0.17Ω
Calculate Resistance
Variables:
- P Power (W)
- V Voltage (V)
- I Current (A)
- R Resistance (Ω)
Example
A 100W bulb at 220V draws current:
I = P/V = 100/220 = 0.455A
Calculate Power
Electromagnetic Waves
Variables:
- c Speed (3×10⁸ m/s)
- f Frequency (Hz)
- λ Wavelength (m)
Example
Radio wave with frequency 100 MHz has wavelength:
λ = c/f = 3×10⁸/100×10⁶ = 3 m
Calculate Wavelength
Variables:
- E Energy (J)
- h Planck’s Constant (6.63×10⁻³⁴ J·s)
- f Frequency (Hz)
Example
Photon of yellow light (λ=600nm) has energy:
f = c/λ = 5×10¹⁴ Hz
E = 6.63×10⁻³⁴ × 5×10¹⁴ = 3.315×10⁻¹⁹ J
Calculate Photon Energy
Wave Optics
Variables:
- β Fringe Width (m)
- λ Wavelength (m)
- D Screen Distance (m)
- d Slit Separation (m)
Example
For λ=600nm, D=1m, d=1mm, fringe width is:
β = (600×10⁻⁹ × 1)/(1×10⁻³) = 0.6 mm
Calculate Fringe Width
Dual Nature of Radiation & Matter
Variables:
- Kmax Max KE (J)
- h Planck’s Constant
- f Frequency (Hz)
- φ Work Function (J)
Example
For metal with φ=2eV, light of λ=300nm:
f = c/λ = 1×10¹⁵ Hz
Kmax = (6.63×10⁻³⁴×1×10¹⁵) – (2×1.6×10⁻¹⁹) = 2.63×10⁻¹⁹ J
Calculate Max KE
Variables:
- λ Wavelength (m)
- h Planck’s Constant
- p Momentum (kg·m/s)
Example
Electron with energy 100eV has wavelength:
p = √(2mE) = √(2×9.1×10⁻³¹×100×1.6×10⁻¹⁹)
λ = 6.63×10⁻³⁴/p = 1.23×10⁻¹⁰ m
Calculate de Broglie Wavelength
Atoms & Nuclei
Variables:
- En Energy of nth level (eV)
- n Quantum Number
Example
Energy of electron in ground state (n=1):
E₁ = -13.6 eV
Energy emitted in transition from n=3 to n=2:
ΔE = 13.6(1/4 – 1/9) = 1.89 eV
Calculate Energy Level
Variables:
- N Nuclei at time t
- N₀ Initial nuclei
- λ Decay Constant
- t Time
Example
Half-life T½ = ln2/λ = 0.693/λ
For carbon-14, T½=5730 years, λ=3.84×10⁻¹² s⁻¹
Calculate Remaining Nuclei
Electronic Devices
Variables:
- IE Emitter Current
- IB Base Current
- IC Collector Current
Example
For transistor with β=100, if IB=10μA:
IC = βIB = 1mA
IE = IC + IB = 1.01mA
Calculate Transistor Currents
Communication Systems
Variables:
- Am Modulated Amplitude
- Ac Carrier Amplitude
- ma Modulation Index
- ωm Modulating Frequency
Example
For ma = 0.8, sideband frequencies are fc ± fm
Bandwidth = 2fm
