Definition and Units of Electric Current
- An electric current is a flow of charged particles through a conductor or space.
- It is defined as the net rate of flow of electric charge through a surface.
- The charge carriers in electric circuits are often electrons or ions.
- In the International System of Units (SI), electric current is expressed in units of ampere (A).
- The ampere is an SI base unit and electric current is a base quantity in the International System of Quantities (ISQ).
- Current intensity is commonly referred to as current itself.
- The unit of current is the ampere (A).
- Current is defined as the rate of flow of electric charge.
- It represents the movement of electrons through a conductor.
- Current can be either direct current (DC) or alternating current (AC).

Symbol and Conventions of Electric Current
- The conventional symbol for current is 'I'.
- It originates from the French phrase 'intensité du courant' (current intensity).
- The direction of conventional current is arbitrarily defined as the direction in which positive charges flow.
- Electrons, the charge carriers in an electrical circuit, flow in the opposite direction of conventional current.
- The reference direction of current is usually assigned arbitrarily in circuit analysis.
- The first step in the analysis is assuming reference directions for the unknown currents.
- Reference directions are necessary for determining the direction of current flow in a circuit.
- This assumption simplifies the analysis of circuit equations and helps in solving for the unknown currents.
- Reference directions can be chosen arbitrarily, but consistency is important throughout the analysis.
- Once the reference directions are established, the circuit equations can be formulated and solved.

Ohm's Law
- Ohm's law states that the current through a conductor is directly proportional to the potential difference across it.
- The mathematical equation for Ohm's law is I = V/R, where I is the current, V is the potential difference, and R is the resistance.
- The resistance in Ohm's law is constant and independent of the current.
- Ohm's law is used to calculate the current in a circuit based on the voltage and resistance.
- It is a fundamental principle in electrical engineering.

Alternating and Direct Current
- Alternating current (AC) periodically reverses the direction of electric charge movement.
- AC is commonly used for electric power delivery and transmission.
- The waveform of an AC power circuit is usually a sine wave.
- Direct current (DC) refers to the movement of electric charge in only one direction.
- DC is produced by sources like batteries and solar cells, and it can be converted from AC using a rectifier.

Occurrences and Measurement of Electric Current
- Natural occurrences of electric current include lightning, static electric discharge, and the solar wind.
- Man-made occurrences include the flow of conduction electrons in power lines and electronic equipment.
- Eddy currents occur in conductors exposed to changing magnetic fields.
- Electric currents also occur in conductors exposed to electromagnetic waves.
- Electric current can be measured using an ammeter or a galvanometer.