- Electric current is the rate at which electric charge flows through a cross-section of a conductor.
- If charge Q passes in time t, the average current is I = Q/t.
- For a continuously changing current, the instantaneous current is I = dQ/dt.
- The SI unit of current is the ampere (A).
- 1 ampere = 1 coulomb per second, or 1 A = 1 C s⁻¹.
- Current is treated as a scalar quantity in circuit theory, although its direction is shown by an arrow.
- Conventional current is taken in the direction in which positive charge would move.
- In a metallic conductor, electrons drift opposite to the direction of conventional current.
Current Density
- Current density (J) is the current passing per unit cross-sectional area normal to the flow.
- For uniform flow, J = I/A.
- Its SI unit is ampere per square metre (A m⁻²).
- Current density is a vector quantity directed along the conventional motion of positive charge.
- In a conducting material, the microscopic relation is J = nqvₙ, where n is carrier number density, q is charge and vₙ is drift velocity.