[Physics Class Notes] on Electric Charge Pdf for Exam

Atoms are the constituents of matter. Atoms are electrically neutral because the number of electrons is equal to the number of protons. Protons do carry a positive charge, whereas electrons have an equal negative charge. Photos are located in the central part of an atom, called a nucleus, along with the electrically neutral neutrons. Protons are bound with the nucleus.

An electron carries a negative charge and revolves around the nucleus in a definite orbit. The magnitude of electric charge of an electron and a proton are equal but are opposite in nature. Typically, the matter is electrically neutral because it is made up of electrically neutral particles or atoms. 

Electric Charge Definition

Just like protons, the electrons are also bound in an atom, but not all electrons. The electrons which are located farther from the nucleus can be removed from the atom. When some electrons are removed from the atom, the number of protons becomes higher than the number of electrons due to a deficit in electrons. After the removal of electrons, the electrically neutral body becomes positively charged.

 

In the opposite case, the body can also acquire electrons from an outside source. In this case, the number of electrons in the body increases, and it becomes negatively charged. 

The deficit or surplus of electrons in a body is called an electric charge.

 

Points to be Noted when Studying Electric Charge

• The protons are positively charged

• The electrons are negatively charged

• The neutrons have no charge

 

Unit of Electric Charge

The unit of Electric Charge is Coulomb. And the value of one coulomb is the amount of charge transferred in one second. Mathematically it is represented as Q = I.t. Q is the symbol for Electric Charge.

 

The matter is always positively charged, negatively charged, or neutrally charged. A charge is denoted by ‘q’, and the SI unit of electric charge is Coulomb. The charge of a particle is basically the cumulative charges of all the electrons present in it. Mathematically it is represented as

Q = ne

where,

q = charge,

n = number of electrons, and

e = charge on 1 electron which is 1.6 × 10^-19C. This is the  electric charge value on an electron. The two basic natures of electric charge are

• Like charges repel each other.

• Unlike charges, they attract each other.

This means that the protons repel protons, while they attract electrons. Similarly, the electrons repel electrons, and they attract protons. The forces acting on a charge are directly associated with the nature of the charge. The magnitude of the charge on an electron and a proton is the same, and it is 1.6 × 10^-19C. The charge on an electron is negative ‘-‘, the charge on a proton is positive ‘+’.

 

Properties of Electric Charge

Various properties of charge are given below:

• Additivity of Electric Charge

• Conservation of Electric Charge

• Quantization of Electric Charge

 

In an isolated system, the electric charge is conserved, which means the net electric charge of a system remains constant. Also, the algebraic sum of the fundamental charges in any isolated system remains the same.

• Electric charge is additive.

• An electric charge is a conserved quantity.

• Electric charge can be quantized.

• Due to the presence of an electric charge, a body either attracts or repels another body based on the nature of the charge.

• Friction between two different types of objects produces a positive charge on one object and a negative charge on another object. When the glass is rubbed with plastic, the glass gains excess electrons and becomes negatively charged, whereas the plastic loses electrons and becomes positively charged.

• Like charges repel each other, i.e., positive charges repel positive charges and negative charges repel negative charges.

• Unlike charges that attract each other, i.e., positive and negative charges attract each other.

• Repulsion is the sure test to determine the nature of a charge on a body.

Types of Electric Charge

There are two kinds of electric charges:

• Positive charge

• Negative charge

 

Negative Charge

If an object has more electrons than protons, it has a negative charge. When an object gains some electrons, the number of electrons in the object becomes greater than the number of protons, and hence it becomes negatively charged.

 

Positive Charge

If there are more protons than electrons in an object, then the object has a positive charge. When an object loses some electrons, the number of protons in the object becomes greater than the number of electrons. Hence, the object becomes positively charged.

 

When the number of positive and negative charges is the same, the negative and positive charges cancel each other out and the object becomes neutral.

 

When a matter is placed into an electric or magnetic field it experiences a certain force, this property of matter is known as electric charge. An electric charge is linked to an electric field and the moving electric charge generates a magnetic field. The combination of electric and magnetic fields is called the electromagnetic field. Interaction between charges generates an electromagnetic force which is the foundation of Physics.

 

How is Electric Charge Measured?

Electric charge is measured in the unit of Coulomb. A charge is said to be 1 coulomb when a current of 1 ampere flows through a unit cross-sectional area for one second. The electric charge formula is given by:

Q = I.t

Where,

• Q = electric charge

• I = electric current

• t = time.

Coulomb’s Law

As we already know that like charges repel each other and
unlike charges attract each other. But do you know how strong these forces actually are? Coulomb’s Law provides a way to calculate the strength of the force between two points.

 

According to the Coulomb’s Law:

The magnitude of the electrostatic force of attraction or force of repulsion between two point charges is directly proportional to the product of the magnitudes of charges and inversely proportional to the square of the distance between the charges.

 

The expression of Coulomb’s Law is :

[F_e = frac{kq_1q_2}{r^2}]

 

where Fe is the electric force, q₁ and q₂ are electric charges, k is the Coulomb’s constant (8.988×109 N⋅m²/C² )  and r is the distance between two points.