Electric current is defined as a rate of flow of charge of the conductor. Electric current exists when there is a net flow of electric charge through the circuit. This charge carried by electrons moving through a conductor. In electrolyte, it can be carried by ions also. In ionized gas or plasma, the current can be flowed by both ions and electrons.

The device used to measure only current known as an ammeter.

## Unit of Electric Current

In general, an electric current is denoted as **‘I’**. The ‘I’ symbol used by **André-Marie Ampère**. The unit of electric current is **ampere** (A).

One ampere is defined as the flow of electric charge across the conductor at the rate of one coulomb per second.

## Electric Charge (Carrier)

The moving charged particle causes the electric current. These moving charges known as a charge carrier. According to the number of charge carriers, it is classified as a majority charge carrier and minority charge carrier.

In conductors or metals, each atom loose electrons from their outer orbit, and can move freely within the metal. Here, the electrons are charge carriers.

Electrons are negative charge carrier and holes are positive charge carriers. A flow of positive charge carriers also creates the same electric current and will give the same effect in a circuit. Therefore, current can be caused by either a positive or negative charge carrier or both.

## Electric Current Formula

According to ohm’s law, the current passing through the circuit is directly proportional to the potential difference between two points.

The proportionality constant gives a value of resistance R. Therefore, the equation of current formulated as;

According to the definition of electric current, it is a flow of rate of charge. So, the equation of current is;

## Direction of Electric Current

There are two theories behind the direction of electric current. One known as conventional current flow and the other is the actual flow of current.

Before the invention of electrons, **Benjamin Franklin** says that the direction of current flows from higher potential to lower potential. Therefore, the current flows from the positive terminal to the negative terminal. This direction of current is known as the conventional direction of the current.

But after the invention of electrons, it is cleared that current flows from the negative terminal to the positive terminal. This direction is the actual direction of the current.

In general, we use a conventional direction of flow for the current. Because it does not make much difference. The negative charge flowing in one direction is equivalent positive charge flowing in the opposite direction.

Therefore, we can either consider that current will flow from positive to negative or vice versa, it will not create a difference in circuit analysis.

## Type of Electric Current

In late 1880 and early 1890, the war of current introduced for competing choose the type of electric current for the power transmission systems.

In this war, one side is **Thomas Edison** and he supports the **DC current**. **Nikola Tesla** and **George Westinghouse** is the other side of this war and winner of this war. They support **AC current**.

So, there are two types of current Direct Current (DC) and Alternating Current (AC).

In alternating current, the direction of current reverses periodically. It is depending on the supply frequency. The AC current is useful to transmit electric power for long-distance. There are many shapes of alternating current. Most commonly used shape is sine, triangular, and square wave.

The DC current is a unidirectional flow of current. So, in DC current, the movement of electric charge is only in one direction. The source of DC current is a battery, thermocouples, solar cells, and commutator type electric machines. An old name of this current is galvanic current.

## Current Density

Current density is nothing but a rate of charge passes through a chosen unit area. It is a vector quantity. Hence, it has direction as well as magnitude.

The magnitude of current density is a ratio of current to unit cross-sectional area. The direction of the current density considered the same as the direction of the current.

The current density is denoted as ‘J’. And the unit of current density is ampere per square meter.

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