1. Current, Voltage, Resistance and Induction

Defining Electric Current

Let us now define electric current and also know about conductors and insulators.

Electric Current is the rate of flow of electrons in a conductor. The SI Unit of electric current is the Ampere.

Electrons are minute particles that exist within the molecular structure of a substance. Sometimes, these electrons are tightly held, and the other times they are loosely held. When electrons are loosely held by the nucleus, they are able to travel freely within the limits of the body. Electrons are negatively charged particles hence when they move a number of charges moves and we call this movement of electrons as electric current. It should be noted that the number of electrons that are able to move governs the ability of a particular substance to conduct electricity. Some materials allow current to move better than others. Based on the ability of the material to conduct electricity, materials are classified into conductors and insulators.

Conductors: these materials allow the free flow of electrons from one particle to another. Conductors allow for charge transfer through the free movement of electrons. The flow of electrons inside the conducting material or conductor generates an electric current. The force that is required to drive the current flow through the conductor is known as voltage.

Examples of conductors: Human body, aqueous solutions of salts and metals like iron, silver and gold.

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.

Examples of Insulator: Plastic, Wood and Glass.

Prerequisites for the Current to Flow in a Conductor

Some of the prerequisites for the electric current to flow in a conductor are discussed here. The circuit includes an energy source (a battery, for instance) that produces voltage. Without voltage, electrons move randomly and are undirected; hence current cannot flow. Voltage creates pressure on the electrons which channelizes it to flow in a single direction.

The circuit forms a closed conducting loop through which electrons can flow. A circuit is said to be closed or complete when a switch is turned ON.

What is an Electromotive Force?

The motion of free electrons is normally haphazard. If a force acts on electrons to make them move in a particular direction, then up to some extent random motion of the electrons will be eliminated. An overall movement in one direction is achieved. The force that acts on the electrons to make them move in a certain direction is known as electromotive force and its quantity is known as voltage and is measured in volts.

Unit of Electric Current

Let us know what is current and the unit to measure it.

The magnitude of electric current is measured in coulombs per second. The SI unit of electric current is Ampere and is denoted by the letter A. Ampere is defined as one coulomb of charge moving past a point in one second. If there are 6.241 x 1018 electrons flowing through our frame in one second then the electrical current flowing through it is ‘One Ampere.’

The unit Ampere is widely used within electrical and electronic technology along with the multipliers like milliamp (0.001A), microamp (0.000001A), and so forth.

Visualizing Electric Current

To gain a deeper understanding of what an electric current is and how it behaves in a conductor, we can use the water pipe analogy of electricity. Certainly, there are some limitations but they serve as a very basic illustration of current and current flow.

Water Pipe Analogy of Electricity

We can compare the electric current to the water flowing through the pipe. When pressure is applied to one end of the pipe, the water is forced to flow through the pipe in one direction. The amount of water flow is proportional to the pressure placed on the end. This pressure can be compared to the electromotive force.

Conventional Current flow Vs Electron Flow

There is a lot of confusion around conventional current flow and electron flow. In this section, let us understand their differences.

Conventional Current Flow vs Electron Flow

Conventional Current Flow 

The conventional current flow is from positive to the negative terminal and indicates the direction that positive charges would flow.

Electron Flow

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

Properties of Electric Current

After we define electric current, let us learn the 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

After defining electric current, let us learn various 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


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

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