Category: 2. Production of Electric charge

When a voltage is applied to a conductor or semiconductor, electric current starts flowing.

In conductors, positively charged protons are held in a fixed position and the negatively charged electrons move from one place to another place by carrying the charge. Thus, electrons conduct electric current in conductors.  

In semiconductors, both free electrons and holes carry charge from one place to another place. Thus, electrons and holes conduct electric current in semiconductors.

When voltage is applied, the electrons (negative charges) move from negative end of the battery to the positive end of the battery. So the electrons (negative charges) current direction is from negative to positive.

On the other hand, holes (positive charges) move from positive end of the battery to the negative end of the battery. So the holes (positive charges) current direction is from positive to negative.

The conventional current direction is from positive to negative (same as the current direction of positive charges).

The charge of a positively charged particle (hole) is equal to the charge of a negatively charged particle (free electron) but opposite in polarity.

A flow of negative charges in a circuit will produce the current same as the flow of positive charges produce. So it does not matter whether the current is flowing from positive to negative or negative to positive, the generated current will be same.

The SI unit of electric current is ampere, which is named after the French physicist Andre-Marie Ampere. The electric current flowing in a conductor or semiconductor is measured in amperes. Ampere is also sometimes referred to as amps or A.

The current flowing through an electronic component (eg: diode) in a circuit is measured by using a device called an ammeter.

Atoms are the basic building blocks of matter. Every object in the universe is made up of atoms. Atoms are the tiny particles. Their size is in nanometers.

Each atom consists of subatomic particles such as electrons, protons, and neutrons. These subatomic particles are smaller than the atom.

Electrons are the negatively charged particles, protons are the positively charged particles, and neutrons are the neutral particles (no charge).

Protons and neutrons are much heavier than electrons. So the protons and neutrons always reside at the center of the atom. The strong nuclear force between the protons and neutrons make them always stick together.

Protons have positive charge and neutrons have no charge. So the overall charge of the nucleus is positive.

Electrons always revolve around the nucleus because of the electrostatic force of attraction between them.

The electrons revolve around the nucleus in different orbits. Each orbit has an energy level associated with it.

The electrons revolving at a close distance from the nucleus have very low energy. On the other hand, the electrons revolving at a greater distance from the nucleus have very high energy.

The electrons in the outermost orbit of an atom are called valence electrons. These electrons are very loosely attached to the parent atom. So applying a small amount of energy is enough to make them free from the parent atom.

When a small amount of energy in the form of heat, light, or electric field is supplied to the valence electrons, they gain sufficient energy and then separated from the parent atom.

The electrons that are separated from the parent atom are known as free electrons. These electrons move freely from one place to another place.

We know that electrons have a negative charge. So the free electrons carry negative charge from one place to another place.

We know that electric current means a flow of charge. So the electrons moving freely from one place to another place will conduct electric current.

In semiconductors, both free electrons and holes are present. Free electrons are the negatively charged particles. So they carry a negative charge (electric current). Holes are the positively charged particles. So they carry a positive charge (electric current).

Thus, both free electrons and holes conduct electric current in semiconductors.

In conductors, holes are negligible. So the free electrons conduct electric current.

Protons also have the ability to conduct electric current. However, protons cannot move freely from one place to another place like electrons. They always held in a fixed position. So the protons do not conduct electric current.

Electric charge is the fundamental property of particles such as electrons and protons. Electric charge can neither be created nor destroyed. That means, if there is an electron or a proton then there is a charge. 

Electrons have a negative charge and protons have a positive charge. Protons are much heavier than electrons. However, the charge of a proton is equal to the charge of an electron.

We know that if two opposite charges are placed close to each other they get attracted. On the other hand, if two same or like charges are placed close to each other they get repelled.

When a proton is placed closer to an electron, they get attracted. On the other hand, when two protons or two electrons are placed close to each other, they get repelled.

Electric charge is measured in coulombs (C). One coulomb is the amount of charge transferred by a current of 1 ampere in 1 second. For example, if 4 coulombs (C) of charge passes in 2 seconds, the current = 4 ÷ 2 = 2 amperes (A).

The electric current is represented by a symbol ɪ. The symbol ɪ was used by the French physicist “Andre-Marie Ampere”. The unit of electric current (ampere) is named after him.

The flow of electric charge carriers in a conductor or semiconductor is called an electric current.

In conductors or semiconductors, electric current is conducted by the tiny particles. These tiny particles are known as electric charge carriers.

The electric charge carriers could be electrons, holes, protons, ions etc. However, the electric current is often conducted by electrons and holes.

In conductors, holes are negligible. So electrons conduct electric current. In semiconductors, both electrons and holes are present. So both electrons and holes conduct electric current.

Electric current is an important quantity in electronic circuits. When a voltage is applied across the conductor or semiconductor, electric current starts flowing. Electric current is often referred to as “current”, for simplicity.

Generally, current means a flow of something from one place to another place. For example, water falling from a hill, river water moving from one place to another place, and ocean water moving from one place to another place are known as water currents. In a river and ocean, the water molecules moving from one place to another place will conducts current.

In a similar way, the electric charge carriers moving from one point to another point in a conductor or semiconductor will conducts electric current.