Electric Charge - Definition, Properties, Formula, Types, Unit, FAQs

We often observe a spark or hear a crackling sound, when we take off our woollen or synthetic clothes. Apart from this, sometimes we experience a sensation of a light shock while opening the door of the car after sliding from the seat. It happens due to the discharge of electric charges through our body, which accumulate due to rubbing against the clothes or the material of the car seat. The electricity developed on objects, when they are rubbed with each other, is called frictional electricity. The electric charges so developed cannot move from one part of the object to the other part. For this reason, frictional electricity is also known as static electricity or electrostatics. Electrostatics deals with the study of forces, potentials and fields arising from static charges i.e. charges at rest.

In this article, we will cover the concept of Electric Charge. This concept falls under the broader category of Electrostatics which is a crucial chapter in Class 12 physics. It is not only essential for board exams but also for competitive exams like the Joint Entrance Examination (JEE Main), National Eligibility Entrance Test (NEET), and other entrance exams such as SRMJEE, BITSAT, WBJEE, BCECE and more.

What is the Electric Charge?

It is observed that glass rods rubbed with wool or silk repel each other and attract lighter objects like paper. Similarly, silk and woollen cloth also repel each other and glass rods and wool attract each other. Similarly, plastic rods rubbed with cats' fur repel each other. The plastic rod attracts a glass rod and repels wool and silk. From the above observation, it was concluded by scientists that by rubbing glass rods, silk, wool and plastic rods are electrified or charged.

The charge is the property associated with the matter due to which it produces and experiences the electrical and magnetic effects.

From observations, the scientist has concluded that the plastic rod has accrued a kind of charge and the glass rod has accrued another kind of charge. That is electric charges are of two types, namely positive charge and negative charge. A body is called to be positively charged when the body loses electrons and negatively charged when the body gains electrons.

Electric charge is a scalar quantity and its SI unit is Coulomb represented as C. C= 1 ampere-second. The dimension of charge is [AT].

Like charges repel each other (glass rods rubbed with wool or silk repel each other) and unlike charges attract each other (glass rod and wool attract each other).

What is Point charge?

If the size of charged bodies is too small compared to the distance between them we treat them as a point charge.

Properties of charge:

1. Additivity: If a system contains n charge $q_1, q_2, q_3 \ldots \ldots q_n$, then the total charge of the system is $q_1+q_2+\ldots \ldots q_n$.

2. The charge is conserved: The charge can be neither created nor destroyed. When we rub a glass rod with silk there is a transfer of charge and not creation. The total charge of an isolated system is always conserved.

3. The charge is independent of the velocity of the particle. I.e The charge is non-relativistic.

4. Quantization: The charge on a body will be some integral multiple of e, where e is the charge of the electron.

$e=1.6 \times 10^{-19} \mathrm{C}$

Watch the Video Below to Understand Better Electric Charge

Solved Examples Based on Electric Charge

Example 1: Charge on $\alpha$-particle is:

1) $4.8 \times 10^{-19} \mathrm{C}$
2) $1.6 \times 10^{-19} \mathrm{C}$
3) $3.2 \times 10^{-19} \mathrm{C}$
4) $6.4 \times 10^{-19} \mathrm{C}$

Solution:

Electric charge

It is the property associated with matter due to which it produces and experiences electrical and magnetic effects.

Alpha particles have a charge of +2,

Hence, the charge on an alpha particle is twice the electron charge =2×1.6×10⁻¹⁹C

q=3.2×10⁻¹⁹

Hence, the answer is the option (3).

Example 2: Which of the following charges is not possible?
1) $1.6 \times 10^{-18} \mathrm{C}$
2) $1.6 \times 10^{-19} \mathrm{C}$
3) $1.6 \times 10^{-20} \mathrm{C}$
4) None of these

Solution:

$1.6 \times 10^{-20} \mathrm{C}$, because this is $\frac{1}{10}$ of electronic charge and hence not an integral multiple.

Hence, the answer is the option (3).

Example 3: When 10¹⁹ electrons are removed from a neutral metal plate, the electric charge on it is

1) $ -1.6 C$
2) $+1.6 C$
3) $10^{+19} \mathrm{C}$
4) $10^{-19} \mathrm{C}$

Solution:

Electric charge -The loss of electrons gives a positive charge.

By using

$Q=n e \Rightarrow Q=10^{19} \times 1.6 \times 10^{-19}=+1.6 C$

Hence, the answer is the option (2).

Example 4: When a body is earth-connected, electrons from the earth flow into the body. This means the body is

1) Unchanged

2) Charged positively

3) Charged negatively

4) An insulator

Solution:

When a positively charged body is connected to the earth, electrons flow from the earth to the body and the body becomes neutral.

Example 5: A conductor has $14.4 \times 10^{-19}$ coulombs positive charge. The conductor has (Charge on electron $=1.6 \times 10^{-19}$ coulombs )

1) 9 electrons in excess

2) 27 electrons in short

3) 27 electrons in excess

4) 9 electrons in short

Solution:

Electric charge

The loss of electrons gives a Positive charge

A positive charge shows the deficiency of electrons.

Number of electrons $=\frac{14.4 \times 10^{-19}}{1.6 \times 10^{-19}}=9$

Hence, the answer is the option (4).

Summary

Electric charge is a basic characteristic of matter that enforces a force on it when it is in an electromagnetic field. Charges come in two forms: positive and negative. Just as charges tend to repel, whereas charges of opposite signs move towards each other. Coulomb’s law explains why objects having charges either attract or repel each other. Electric charge is quantized; this means that it exists in certain fixed quantities and particles such as electrons are responsible for carrying it.