current electricity current electricity formula sheet for CBSE, NEET, IIT-JEE, IB, IGCSE and A-Level Physics is given here with symbols, units, graphs, memory tricks and revision cards.
If Current Electricity formulas, derivations, Wheatstone Bridge, Meter Bridge, Potentiometer, Kirchhoff's Rules, Drift Velocity or NEET/JEE numericals are not clear, students may contact Kumar Sir for one-to-one Physics guidance. Contact: +91-9958461445 | Website: KumarPhysicsClasses.com

Formula Handbook | Current Electricity | Class 12

Current Electricity Complete Formula Sheet

CBSE Class 12 • NEET • JEE Main • JEE Advanced • IB Physics • IGCSE • ICSE • A-Level Physics

Formula CardsSVG GraphsMemory TricksPrintable Poster

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1-5. Current, Current Density, Drift Velocity, Mobility And Ohm's Law

Electric Current

I = Q/tI = dQ/dt

I: current, Q: charge, t: time. Unit: ampere. Dimension: [A]. Conventional current is opposite to electron flow.

Current Density

J = I/AJ = nqv_d

J: current per unit area, n: carrier number density, q: charge, v_d: drift velocity.

Drift Velocity

v_d = I/nqAv_d = eEτ/m

Average velocity gained by charge carriers under electric field. τ is relaxation time.

Mobility

μ = v_d/Eμ = eτ/m

Mobility measures how easily charge carriers move in an electric field.

Ohm's Law

V = IRI = V/RR = V/I

Valid when temperature and physical conditions remain constant.

Microscopic Ohm's Law

J = σEE = ρJ

σ is conductivity and ρ is resistivity.

6-9. Resistance, Resistivity, Conductivity And Temperature Dependence

Resistance

R = ρL/A

Depends on length, area, material and temperature.

Resistivity

ρ = RA/L

Material property. Does not depend on length, area, shape or size; depends on material and temperature.

Memory Card

Resistance changes with dimensions. Resistivity does not.

Conductivity

σ = 1/ρσ = nq²τ/m

Higher conductivity means lower resistivity.

Temperature

R_T = R₀(1 + αΔT)R_T = R₀(1 + αT)

α is temperature coefficient. Metals: positive α. Semiconductors: negative α. Alloys: small α.

Conductivity Relation

σ = neμ

Since μ=eτ/m, σ=ne(eτ/m)=ne²τ/m.

10-11. Electrical Energy And Power

Electrical Energy

W = VItW = I²RtW = V²t/R

Unit: joule. Commercial unit: kWh. 1 kWh = 3.6 x 10⁶ J.

Electrical Power

P = VIP = I²RP = V²/R

Power is energy per second.

AC Average Power

P_avg = V_rmsI_rmscosφ

cosφ is power factor.

12-16. Cells, EMF, Internal Resistance And Kirchhoff's Rules

Cell And EMF

V = E - Ir

E is EMF, V is terminal voltage, r is internal resistance. Open circuit: I=0, V=E. Short circuit: I=E/r.

Internal Resistance

r = R[(l₁-l₂)/l₂]r = R(l₁/l₂ - 1)

Potentiometer method.

Maximum Power Transfer

R = r

External resistance equals internal resistance.

Cells In Series

E_eq = nEr_eq = nrI = nE/(R+nr)

Cells In Parallel

E_eq = Er_eq = r/nI = E/(R+r/n)

Kirchhoff's Rules

ΣI_in = ΣI_outΣV = 0

KCL: charge conservation. KVL: energy conservation.

17-19. Wheatstone Bridge, Meter Bridge And Potentiometer

Wheatstone Bridge

P/Q = R/SPS = QR

At balance, galvanometer current is zero and V_B=V_D.

Meter Bridge

R/X = l/(100-l)X = R(100-l)/l

Best balance: 40 cm to 60 cm.

Potentiometer

k = V/LV = klE₁/E₂ = l₁/l₂Sensitivity ∝ 1/k

20. Important SVG Graphs

21-25. Confusions, Memory Tricks And Rapid Revision

Resistance vs Resistivity: R depends on dimensions; ρ is material property.

Current Density vs Drift Velocity: J = nqv_d; v_d is carrier speed.

EMF vs Terminal Voltage: E is source energy per charge; V=E-Ir while discharging.

Power vs Energy: Power is rate; energy is power multiplied by time.

Mobility vs Conductivity: μ is carrier response; σ depends on n, e and μ.

Meter Bridge vs Wheatstone: Meter bridge is practical Wheatstone bridge with wire length ratio.

Current: charge per second.

Drift velocity: current divided by charge carriers.

Conductivity: reciprocal of resistivity.

Power: energy per second.

Potentiometer: smaller k means more sensitivity.

Bridge: null current means balance.

26. Printable Formula Wall Poster

Topic	Must-Remember Formulas
Current	I=Q/t, I=dQ/dt, J=I/A, J=nqv_d
Drift/Mobility	v_d=I/nqA, v_d=eEτ/m, μ=v_d/E=eτ/m
Ohm/Material	V=IR, R=ρL/A, ρ=RA/L, σ=1/ρ=nq²τ/m, J=σE
Temperature	R_T=R₀(1+αΔT)
Energy/Power	W=VIt=I²Rt=V²t/R, P=VI=I²R=V²/R
Cells	V=E-Ir, series: I=nE/(R+nr), parallel: I=E/(R+r/n)
Bridge/Potentiometer	P/Q=R/S, X=R(100-l)/l, E=kl, E1/E2=l1/l2, r=R(l1/l2-1)

Need Help With Current Electricity Formulas?

If Current Electricity formulas, derivations, Wheatstone Bridge, Meter Bridge, Potentiometer, Kirchhoff's Rules, Drift Velocity or NEET/JEE numericals are not clear, students may contact Kumar Sir for one-to-one Physics guidance.

Phone: +91-9958461445
Website: KumarPhysicsClasses.com

Contact Kumar Sir