Current Electricity — Formula Sheet

I = \frac{\Delta q}{\Delta t}

I = nAev_d

V = IR

R = \rho \frac{l}{A}

\rho = \frac{m}{ne^2\tau}

R_s = R_1 + R_2 + \dots

\frac{1}{R_p} = \frac{1}{R_1} + \frac{1}{R_2} + \dots

\rho = \rho_0 [1 + \alpha (T - T_0)]

R = R_0 [1 + \alpha (T - T_0)]

Current is measured in amperes (A)

1 A = 1 coulomb per second.

In series

same current flows through all resistors; equivalent resistance is sum: R_eq = R₁ + R₂ + ...

In parallel

same voltage across all resistors; reciprocal of equivalent resistance is sum of reciprocals: 1/R_eq = 1/R₁ + 1/R₂ + ...

Resistance of metals increases with temperature

R = R₀[1 + α(T − T₀)].