** Current Electricity – Notes **

**Electric current**

A steady current is positive when it moves in the forward direction, that is, left to right and it is negative when it moves in the backward direction, that is, right to left.

Instantaneous current at any time t is expressed as: I (t) = lim┬(t→0 )〖ΔQ/Δt〗

The SI unit of current is ampere (A).

Materials, whose electrons are totally bound to their nuclei and cannot be separated even on applying an electric field, are called insulators.

Materials which have some free electrons, which are practically free to move within the bulk material, are called conductors.

Electrolytic solutions are also categorized as conductors as both positive and negative charges move when an electric field is applied.

**Ohm’s Law**

Current per unit area is called current density (j), expressed as j = E/ρ

The SI unit of current density (j) is *A/m ^{2}*