Current Electricity — Chapter Summary

Current is the net charge passing

Current is the net charge passing through a cross-section per unit time. For steady current, I = q/t. For a changing current, I(t) = lim_{Δt→0} ΔQ/Δt.

Current is a scalar quantity

Current is a scalar quantity, even though it is represented by an arrow in circuit diagrams. Direction is shown for convenience, but currents do not o

For a uniform conductor

For a uniform conductor, R = ρl/A. Resistance depends on length and cross-sectional area, while resistivity depends only on the material. The SI unit

Ohm's law states V = RI

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

In an electric field

In an electric field, electrons accelerate between collisions and acquire an average drift velocity v_d = -eEτ/m. The current density is j = (ne²/m)τE