Current Electricity — Formula Sheet

Current I = dQ/dt, measured in Amperes (A); 1 A = 1 C/s

Ohm's law (microscopic form)

J = σE, where σ is conductivity and E is electric field

Resistance R = V/I with SI unit Ohm (Ω); 1 Ω = 1 V/A

Equivalent resistance in series

R_s = R₁ + R₂ + R₃ + ...

Terminal voltage

V = ε - Ir, where ε is emf, I is current, r is internal resistance

Resistors can be connected in series (RS = R1 + R2 + R3...) or parallel (1/RP = 1/R1 + 1/R2 + 1/R3...).