Current Electricity — Formula Sheet

I = q/t

I(t) = lim_{Δt→0} ΔQ/Δt

V = RI

R = ρl/A

j = I/A

E = jρ

j = σE

v_d = -eEτ/m

j = (ne²/m)τE

σ = ne²τ/m

μ = |v_d|/E = eτ/m

ρ_T = ρ_0[1 + α(T − T_0)]

α > 0 for metals

For steady current, current is defined by I = q/t.

For a uniform conductor, R = ρl/A.

Ohm's law states V = RI for many conductors under suitable conditions, and in vector form j = σE or E = jρ.

In an electric field, electrons accelerate between collisions and acquire an average drift velocity v_d = -eEτ/m.