Electric current

Electric current is a fundamental concept in electricity. It describes the movement of electric charge through a conductor, such as a metal wire.

Flow of Charge Carriers

An electric current is caused by the flow of charge carriers. In metals, these charge carriers are electrons. In ionic solutions, the charge carriers can be positive or negative ions. The direction of conventional current is defined as the direction in which positive charges would flow, even though in metals, electrons (which are negatively charged) move in the opposite direction.

Quantisation of Charge

The charge on charge carriers is quantised. This means that charge exists in discrete packets, not as a continuous value. The smallest possible charge is the elementary charge, $e$, which is the charge of a single proton (or the magnitude of the charge of a single electron).

Relationship Between Charge, Current, and Time

The amount of charge that passes a point in a circuit is related to the current and the time for which it flows.

Microscopic View: Current in a Conductor

In a conductor, current depends on:

• The number of charge carriers per unit volume ($n$)
• The cross-sectional area of the conductor ($A$)
• The average drift velocity of the charge carriers ($v$)
• The charge on each carrier ($q$)

The current can be calculated using:

Example Calculation

Key Points

• Electric current is the flow of charge carriers.
• Charge is quantised in multiples of the elementary charge, $e$.
• Use $Q = It$ to relate charge, current, and time.
• Use $I = Anvq$ to relate current to microscopic properties of a conductor.