Basic Properties of Electric Charge: Definition, Unit

In this article, we will learn about the charge and Basic Properties of Electric Charge. Electric charge is the basic property of matter just like mass and other properties. We know that matter is made of atoms that consist of electrons, protons, and neutrons. Out of these subatomic particles, electrons and protons carry the charge.

Electric Charge is the property of subatomic particles that causes them to experience a force when placed in an electromagnetic field. The movement of electric charge produces electricity. Continue reading to know more.

What is an Electric Charge?

When we rub a plastic scale on our dry hairs, the scale attracts tiny pieces of paper. This happens because plastic scale acquires charge when it is rubbed with dry hairs. Electric charge is the property of matter that causes it to experience a force when placed in an electromagnetic field. 

Electrons are negatively charged particles, whereas protons carry a positive charge. These two charges are equal and opposite. Neutrons are electrically neutral particles. If the number of electrons in an object is more than the number of protons, then the object is said to be negatively charged. Similarly, when the number of electrons in an object is less than the number of protons, then the object is positively charged.

Definition of Electric Charge

Electric charge is the basic property of matter that causes it to experience a force when placed in an electromagnetic field. It is represented by the letter \({\text{Q}}\). There are two types of electric charge namely positive charge which is present on a proton and negative charge which is present on an electron. 

When an object carries an equal amount of protons and electrons, then it is said to be electrically neutral. The charge \(\left( Q \right)\) on an object is equal to the number of electrons \(\left( n \right)\) times the charge present on one electron \(\left( e \right)\).

\(Q\, = \,ne\)

(The charge on an electron is equal to \(1.6 \times {10^{ – 19}}\,{\rm{C}}\))

Unit of Electric Charge

The SI unit of electric charge is coulomb \(\left({\text{C}} \right).\) The electric charge \(\left( Q \right)\) is equal to the product of the electric current \(\left( I \right)\) and the time \(\left(\ t \right)\) for which the current flows through the wire, so we get

\({\rm{1}}\,{\rm{Coulomb}}\,{\rm{ = }}\,{\rm{1}}\,{\rm{Ampere}}\, \times \,{\rm{1}}\,{\rm{Second}}\)

What are the Basic Properties of Electric Charge?

All objects are made of atoms, which contain negatively and positively charged subatomic particles. Electrons can move from one place to another, but protons cannot move. Generally, the loss or gain of electrons by an object makes it acquire an electric charge. There are some basic properties of electric charge.

1. Like charge repel and unlike charges attract each other

There are two types of electrically charged objects based on the number of electrons they carry. The object which carries more electrons is said to be negatively charged, and the object which carries more protons is said to be a positively charged object. An object acquires a charge by many methods like charging by friction, conduction, or induction. This process imbalances the number of electrons present in an object. For example, when an ebonite rod is rubbed with wool, the ebonite rod gains a negative charge because of the gain of electrons from the wool, and the wool becomes positively charged. 
Rub a plastic ruler with a woollen cloth and suspend it from support with the help of a string. Now rub another plastic ruler with a woollen cloth and bring it near the one which is suspended from a support. You will be able to see that the two rulers will repel each other. If we bring a glass rod rubbed with a silk cloth near the first ruler, the ruler will get attracted towards the glass rod. Similarly, two charged glass rods repel each other when brought close to each other. This activity clearly explains that the two rulers carry the same type of charge, so they repel each other, whereas the glass rod and the ruler carry an opposite charge, so they attract each other.

From here we can conclude that like charges repel each other and unlike charges attract each other.

2. Charge is a conserved quantity

It is not possible to create or destroy the net charge carried by any closed system. There is the transfer of electrons from one object to another object. In some processes, charged particles are produced, but always equal amounts of negative and positive charges are produced. The total amount of positive charge and negative charge before and after any process remains the same. Hence, the algebraic sum of all the electric charges in any closed system is constant.

3. Charges are additive in nature

The electric charge has magnitude, but no direction. The total charge on an object is equal to the algebraic sum of all charges located at different regions of the object. If a system contains two point charges \({q_1}\) and \({q_2},\) then the total charge of the system is obtained by adding algebraically \({q_1}\) and \({q_2}.\)

\(Q\, = \,{q_1} + {q_2}\)

4. Quantization of charge

All charges are integral multiples of a basic unit of charge \(\left( e \right).\) The charge \(\left( Q \right)\) on an object is given by 

\(Q\, = \,ne\)

Where \(n\) is an integer. The basic unit of charge is equal to the charge present on an electron. By convention, the charge present on an electron is taken to be negative and its magnitude is equal to \({\rm{1}}.{\rm{6}} \times {\rm{1}}{{\rm{0}}^{{\rm{ – 19}}}}\,{\rm{C}}{\rm{.}}\)

Methods of Charging a Body

We know that charges can neither be created nor destroyed. They can only transfer from one object to another. There are three methods to charge an object:

1. Charging by friction

When Styrofoam is rubbed with paper, some electrons from the paper get transferred to the Styrofoam. So, the Styrofoam acquires a net negative charge because it gains an excess of negatively charged particles. In this process of rubbing, the paper loses electrons, so it acquired a positive charge. When objects get charged by friction, they acquire equal and opposite charges. The electricity produced in this process is called static electricity or frictional electricity. It is produced by the imbalance of charge within an object.

2. Charging by conduction

We can charge a neutral object by bringing it in contact with another charged body. This process is called charging by conduction. For example, when a positively charged aluminium plate is brought in contact with a neutral metal disc. The metal disc becomes charged. 

3. Charging by induction

The method of charging an object by bringing it near a charged body is called charging by induction. For example, we can charge an electroscope by induction. Suppose we want to charge an electroscope positively, then we will bring a negatively charged balloon near its metal top. As a result of this, positive charges from the electroscope will get accumulated on the metal disc and negative charges will accumulate on the leaves of the electroscope. Now when we touch the leaves, all the negative charges from it will enter the earth and on removing the contact and balloon, the positive charge will redistribute itself throughout the electroscope making it positively charged.

Solved Examples on Basic Properties of Electric Charge

1.How many electrons are there in one coulomb of charge?
Sol: Given, the total charge \(q{\rm{ = 1}}\,{\rm{C}}\)
The charge on one electron, \(e\,{\rm{ = }}\,{\rm{1}}.{\rm{6}} \times {\rm{1}}{{\rm{0}}^{{\rm{ – 19}}}}\,{\rm{C}}\)
Let the number of electrons \(= n\)
\(q = ne\)
\(n{\rm{ }} = \frac{q}{e} = \frac{1}{{1.6 \times {{10}^{ – 19}}}} = 6.25 \times {10^{18}}\)
Therefore, one coulomb of charge contains \(6.25 \times {10^{18}}\) electrons.

2. When \({10^{19}}\) electrons are removed from a neutral metal plate, then calculate the electric charge on it.
Sol: Given, the number of electrons removed from the metal plate, \(n = {10^{19}}\)
The charge on one electron, \(e = 1.6 \times {10^{ – 19}}\,{\rm{C}}\)
Let the electric charge on the metal plate \(= Q\)
\(Q = ne\)
\(Q = {10^{19}} \times 1.6 \times {10^{ – 19}} = 1.6\,{\rm{C}}\)
Therefore, the electric charge on the metal plate is \(1.6\,{\text{C}}.\)

Frequently Asked Questions

Q.1.Which is the true test for electrification?
Ans: Repulsion is the true test for electrification because two objects having an unlike charge attract each other, and a charged object also attracts another uncharged object, but only two objects having opposite charges can push or repel each other.  

Q.2.What is the basic cause of quantization of charge?
Ans: There are two types of electric charges namely negative charge and positive charge. All matter is made of atoms, which consist of electrons, protons, and neutrons. Electrons are considered as negatively charged and protons positively charged. Neutrons have no charge. When two charges are brought close to each other, then they will experience a force. Unlike charges attract each other and like charges repel each other.

Q.4. What are the five basic properties of electric charge?
Ans: The five basic properties of electric charge are as follows:
a. Like charges repel each other and unlike charges attract each other.
b. The electric charge is conserved in a closed system.
c. The electric charge depends only on the magnitude, but not on direction.
d. Electric charges are quantized which means all charges are integral multiples of a basic unit of charge.
e. Electric charges are additive in nature.

Q.5. How do electric charges behave?
Ans: There are two types of electric charges namely negative charge and positive charge. All matter is made of atoms, which consist of electrons, protons, and neutrons. Electrons are considered as negatively charged and protons positively charged. Neutrons have no charge. When two charges are brought close to each other, then they will experience a force. Unlike charges attract each other and like charges repel each other.