Electric charge – definition, formula, properties, unit

Electrostatics Article – 1:

The article series on Electrostatics start with static charges. You can read all articles on electrostatics one by one by clicking on the Next Article button at the end of each article. Electric charge is the basic property of substances. To understand the properties and other facts of an electric charge some branches of Physics like the Electromagnetic field, and current electricity are introduced. But, do you know that all substances are neutral in nature? Charges are created artificially or by natural phenomena. In the article, I’m going explain the Definition, properties, Unit, Dimension, production, and formula for electric charge.

Contents of this article:

  • Definition for electric charge
  • Formula for Electric charge
  • Unit of electric charge
  • Dimension of electric charge
  • How to produce electric charge?
  • Electronic Theory of electricity
  • Properties of electric charge
  • Distribution of electric charges
  • Quantization rule of charge
  • Law of Conservation of Charge

Definition of electric charge

Electric charge is a property of substances (especially of conductors) by which it can produce an Electric field and Magnetic field (if the charge is moving) around it and thereby it can interact with other charges inside these field regions. A static charge produces only an electric field around it whereas a moving charge can produce both an Electric and Magnetic field around it.

One cannot have a single free charge but can have a charged particle. There are two types of charges depending upon their sign –

  1. Positive charges
  2. Negative charges

The formula for Electric charge

The amount of electric charge is equal to the multiplication between the current and the time of current flow. If I amount Current passes through a region for the time t then the amount of charges passing through that region is, Q = It ………….. (1)

This is the basic formula of electric charge that relates it to electric current.

Units of Electric charge:

SI unit of Electric charge is Coulomb (C) and CGS unit is Stat-Coulomb or esu.

1 Coulomb = 3×109 Stat-Coulomb.

Another unit of it is Ampere.second (A.s)

Dimension of Electric charge

The Dimension of Electric charge is [TI]. Sometimes, the dimension of electronic charge is represented as [ M0L0TI ].

How to produce an electric charge?

Surface charge of a Sphere
Electric charge of a Sphere

Generally, every atom has an equal number of protons and electrons. That means every atom is electrically neutral. But we can charge the atoms or the substances. According to the electronic theory of charge if an atom has an excess of electron then it is a negatively charged atom and if an atom has a lack of electron then it is a positively charged atom. A substance can be charged by mainly three processes –

  1. Friction process
  2. Induction process
  3. Conduction process

Production of Electric charge by Friction process

If two different substances are rubbed, atoms of both substances participate in it. We consider the rubbing between two atoms of two different substances (one atom from each).

During the rubbing heat energy is produced due to friction between the atoms. Electrons of the outer shell of atoms absorb this heat energy and get excited.

If the amount of absorbed heat energy exceeds the ionization energy of an atom then electrons emit from that atom and transfer to the other atom of another substance.

The atom with lower binding energy will lose electrons and becomes a positively charged ion. On the other hand, the atom with greater binding energy will gain electrons and becomes a negatively charged ion.

In this way, one can produce electric charges by friction process.

Production of Electric charges by Induction process

One can produce electric charges by induction process also. The charges produced by the induction process are the induced charges. Two metallic bodies can be charged oppositely by this process. We have a separate article on this.

Suggested Article: how to charge two metallic spheres oppositely by induction process.

Electronic Theory of electricity

The electronic theory of electricity states that if an atom losses electrons then it becomes a positively charged ion and if an atom gains electrons then it becomes a negatively charged ion. So, a positively charged object has a deficiency of electrons in its atoms and a negatively charged object has excess electrons in its atoms.

Properties of Electric charge

We already have a separate article on the properties of electric charges. Here we have listed a few of those –

  1. Electric charges can be positive and negative.
  2. They exert force on each other. Charges of the same sign repel and charges of opposite signs attract each other.
  3. Electric charge is a conserved physical quantity. It is a scalar quantity.
  4. Electric charges are quantized in nature. See the quantization rule of the charge.
  5. The amount of charge is independent of its state of rest or motion. So, the amount of charge is invariant with respect to the frame of reference.

Suggested Article: Properties of Electric charges.

Distribution of charges

There are three types of charge distributions –

  1. Line Charge distribution or Linear distribution
  2. Surface charge distribution
  3. Volume Charge distribution

In linear distribution, charges are distributed along a line. The charge distribution along the length of a rod is the linear distribution of charge.

The charge distribution on the surface of a conductor is the surface charge distribution and the charge distribution in the volume of a conductor is the volume charge distribution.

Quantization rule of charge

Quantization means discontinuous. An object cannot have any value of charge on it. The Quantization rule of charge states that the amount of charge carried by an object is always an integral multiple of the charge of an electron.

The charge of an electron is the smallest unit of charge. If – e is the charge of an electron, then an object can have the charge -e, -2e, -3e, -4e, etc. It cannot have a charge in between those numbers.

Law of Conservation of Electric Charge

The principle of conservation of electric charge states that the algebraic sum of the total positive and negative charges in an isolated body is constant everywhere. This is a Universal law.

This is all from this article on basic properties, facts, definition and formula for electric charge. You learned how to give electric charges to a conductor. Do you know these charges are distributed in different ways in conductors? Click on the Next Article button to read about Electric charge distribution in a Conductor.

Thank you!

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