Electric Current – SI Unit, Conventional Direction of Flow & More

What is an Electric current?

Electric current is defined as the rate of flow of negative charges of the conductor. To put it simply, the continuous circulation of electrons in an electrical circuit is called an electrical current. The conducting material consists of a large number of free electrons which move from one atom to the other at random.

SI Unit of Electric Current

Because the charge is measured in coulombs and time in seconds, so the unit of electric current is coulomb/Sec (C/s) or amperes (A). The amperes is the SI unit of the conductor. The ā€œIā€ is the symbolic representation of the current.

Q= 1C

t= 1s


I= 1A


Thus, a wire is said to carry a current of one ampere when charge flows through it at the rate of one coulomb per second.

When an electrical potential difference is used throughout the metal wire, the loosely attached free electrons start moving towards the positive terminal of the cell. This constant circulation of electrons constitutes the electrical current. The circulation of currents in the wire is from the negative terminal of the cell to the positive terminal through the external circuit.

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Conventional Direction of Flow of Current

According to the electron theory, when the potential difference is applied across the conductor some matter flows through the circuit which makes up the electric current. It was considered that this matter flows from higher potential to lower potential, i.e., positive terminal to the negative terminal of the cell through the external circuit.


This convention of the flow of current is so strongly established that it is still in use. Thus, the standard direction of flow of current is from the positive terminal of the cell to the negative terminal of the cell through the external circuit. The magnitude of the flow of current at any section of the conductor is the rate of flow of electrons i.e., charge flowing per second.

Mathematically, it is represented by

I= Q/t

electric-current-equation-1On the basis of the flow of electric charge the current is mainly categorized into 2 types, i.e., alternating current and direct current. In direct current, the charges flow through unidirectional whereas in alternating current the charges flow in both the direction.

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Electron flow

The electron flow is from negative to positive terminal. Electrons are negatively charged and are therefore drawn into the positive terminal as unlike charges attract.

Current is produced by sources such as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type.

Effect of Electric Current

When an electric current flows through a conductor there are a number of signs which tell that a current is flowing.

Heat is dissipated

Potentially the most obvious is that heat is created. If the current is small then the amount of heat generated is likely to be very small and might not be noticed. Nevertheless, if the current is larger then it is possible that an obvious amount of heat is created.

An electric fire is a prime example showing how a current causes heat to be created. The actual quantity of heat is governed not only by the current, however, also be the voltage and the resistance of the conductor.

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Magnetic effect

Another effect that can be noticed is that an electromagnetic field is developed around the conductor. If a current is flowing in the conductor then it is possible to identify this. By putting a compass near to a wire carrying a fairly large amount of direct current, the compass needle can be seen to be deflected.

Note this will not deal with mains because the field is alternating too quickly for the needle to respond and the two wires (live and neutral) close together in the very same cable will cancel out the field.