Definition: Electric Current is defined as the rate of flow of electrons in a conductor. The SI Unit of electric current is the Ampere. In other words, the continuous flow of electrons in an electric circuit is called an electric current.The conducting material consists a large number of free electrons which move from one atom to the other at random.
Ex. of conductors: Human body, steel, iron, copper, Aluminium, silver and gold.
Did you know?
Silver is the best conductor of electricity.
Insulators: Insulators are materials that restrict the free flow of electrons from one particle to another. The particles of the insulator do not allow the free flow of electrons; subsequently, charge is seldom distributed evenly across the surface of an insulator.
Ex. of Insulator: Plastic, Rubber, Wood and Glass
Unit of Current
Since 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 I is the symbolic representation of the current.
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 applied across the metallic wire, the loosely attached free electrons start moving towards the positive terminal of the cell shown in the figure below. This continuous flow of electrons constitutes the electrical current. The flow of currents in the wire is from the negative terminal of the cell to the positive terminal through the external circuit.
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 constitutes 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 flow of current is so firmly established that it is still in use.Thus, the conventional 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 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
On the basis of the flow of electric charge the current is mainly classified into two types, i.e. alternating current and direct current. In direct current, the charges flow through unidirectional whereas in alternating current the charges flows in both the direction.
Properties of Electric Current
Electric current is an important quantity in electronic circuits. We have adapted electricity in our lives so much that it becomes impossible to imagine life without it. Therefore, it is important to know what is current and the properties of the electric current.
- We know that electric current is the result of the flow of electrons. The work done in moving the electron stream is known as electrical energy. The electrical energy can be converted into other forms of energy such as heat energy, light energy, etc. For example, in an iron box, electric energy is converted to heat energy. Likewise, the electric energy in a bulb is converted into light energy.
- There are two types of electric current known as alternating current (AC) and direct current (DC). The direct current can flow only in one direction, whereas the alternating direction flows in two directions. Direct current is seldom used as a primary energy source in industries. It is mostly used in low voltage applications such as charging batteries, aircraft applications, etc. Alternating current is used to operate appliances for both household and industrial and commercial use.
- The electric current is measured in ampere. One ampere of current represents one coulomb of electric charge moving past a specific point in one second.
| 1 ampere = 1 coulomb / 1 second |
- The conventional direction of an electric current is the direction in which a positive charge would move. Henceforth, the current flowing in the external circuit is directed away from the positive terminal and toward the negative terminal of the battery.
Effects of Electric Current
When a current flows through a conductor, there are a number of signs which tell if a current is flowing or not. Following are the most prominent signs:
Heating Effect of Electric Current
When our clothes are crumpled, we use the iron box to make our clothes crisp and neat. Iron box works on the principle of heating effect of current. There are many such devices that work on the heating effect.
When an electric current flows through a conductor, heat is generated in the conductor.
The heating effect is given by the following equation
H=I2RT
The heating effect depends on the following factor:
- The time ‘t‘ for which the current flows. The longer the current flows in a conductor more heat is generated.
- The electrical resistance of the conductor. Higher the resistance, the higher the heat produced.
- The amount of current. The larger the amount of current higher the heat produced.
If the current is small then the amount of heat generated is likely to be very small and may not be noticed. However, if the current is larger then it is possible that a noticeable amount of heat is generated.
Magnetic Effect of Electric Current
Another prominent effect that is noticeable when an electric current flows through the conductor is the build-up of the magnetic field. We can observe this when we place a compass close to a wire carrying a reasonably large direct current, the compass needle deflects. The magnetic field generated by a current is put to good use in a number of areas. By winding a wire into a coil, the effect can be increased, and an electromagnet can be made.
Chemical Effect of Electric Current
When an electric current passes through a solution, the solution ionizes and breaks down into ions. This is because a chemical reaction takes place when an electric current passes through the solution. Depending on the nature of the solution and the electrodes used, the following effects can be observed in the solution:
- change in the colour of the solution
- metallic deposits on the electrodes
- a release of gas or production of bubbles in the solution