Definition and Formula for Electric charge | Unit

Electric charge is the basic property of some substances. To understand the properties and other facts of an electric charge some branches of Physics like Electromagnetic field, current electricity are introduced. In the article “definition and formula of electric charge” we are going to learn the basic things like Definition, Formula, Unit, Dimension, production, and Properties of electric charge.

Contents in this article:

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

Explanation of this article with a video

Discussion on electric charge with a video

Definition of electric charge

Electric charge is a property of some 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 Electric and Magnetic field around it.

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

  1. Positive charges
  2. Negative charges

Electric charge and electronic charge are same things.

Formula for Electric charge

If I amount Current passes through a region for the time t then number of charges passing through that region is,

Q=It …….. (1)

So, the amount of electric charge is the multiplication between the current and the time of current flow.

Units of Electric charge:

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

1 Coulomb = 3×109 statcoulomb.

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?

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 will be negatively charged atom and if an atom has a lack of electron then it becomes a positively charged atom. A substance can be charged by mainly two processes –

  1. Friction process
  2. Induction 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, Electric charges can be produced by friction process.

Production of Electric charges by Induction process

One can also produce electric charges by induction process. The charges produced by the induction process are the induced charges. To produce induced charges we need to follow the following steps –

Production of charge by induction process
Production of charge by induction process
  1. First, we take two spherical conductors. They should not touch the ground or any other conductor. To make sure it, one can insert an insulator between the sphere and its stand.
  2. Now place these two spheres in contact with each other.
  3. Now bring a Charged rod in front of any of the spheres. The rod should not be in contact with the spheres.
  4. As soon as we place the charged rod in front of a sphere, the induction process occurs in the spheres. If the rod is positively charged then negative charge induces in the nearest sphere and positive charge induces in the further sphere.
  5. Now remove one of the spheres without moving the rod. While removing the sphere don’t touch on it, you should catch it below the stand.
  6. After removing one of the spheres, we will get two separate spheres, one with positive charges and the other with negative charges.

In this way, one can charge two conductors with opposite charges at the same time by the induction process of charge.

Electronic Theory of electricity

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

Properties of Electric charge

The properties of electric charges are as followings

  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.

Distribution of charges

There are three types of charge distribution –

  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 be 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

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 the basic properties, facts, definition and formula for electric charge. If you have any doubt on this topic you can ask me in the comment section.

Thank you!

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  6. Surface charge density– definition, unit, formula, dimension
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  8. Electrostatic Potential and Potential energy

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