What is Electric Charge?
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.
FAQs on Electric Charge
1. What is the definition of electric charge and how does it relate to the structure of matter?
Electric charge is a fundamental property of certain subatomic particles that causes them to experience a force when placed in an electric and magnetic field. In matter, protons carry positive charge, electrons carry negative charge, and neutrons are neutral. The balance and transfer of these charges determine the overall charge of an object.
2. How is the SI unit of electric charge defined according to the CBSE Physics syllabus for 2025–26?
The SI unit of electric charge is the coulomb (C). One coulomb is the amount of charge transferred by a current of one ampere flowing for one second, expressed mathematically as Q = I × t, where Q is charge, I is current (in amperes), and t is time (in seconds).
3. What are the basic properties of electric charge every CBSE student should recall for examinations?
The main properties of electric charge are:
- Additivity: The net charge is the sum of individual charges.
- Quantization: Charges occur only in discrete amounts (multiples of elementary charge e = 1.6 × 10-19 C).
- Conservation: Total charge in an isolated system remains unchanged.
- Like charges repel, unlike charges attract.
4. In board examinations, how can students differentiate between positive, negative, and neutral objects in terms of charge?
Objects are positively charged if they have more protons than electrons (electron deficit), negatively charged if they have more electrons (electron surplus), and neutral when the number of protons equals the number of electrons. Exam questions often ask for identification based on this count of fundamental particles.
5. What are some common misconceptions about the nature of electric charge that students should avoid in CBSE exams?
Key misconceptions include:
- Thinking electric charge can be fractional (in reality, it's always in multiples of e).
- Assuming attraction only occurs between opposite charges (induced charges can also attract).
- Believing charge can be created or destroyed (charge is always conserved).
6. Explain the concept of quantization of electric charge and why fractional charges aren't observed in isolation.
Quantization of electric charge means all observable charges exist as integral multiples of the elementary charge (e). Fractional charges are not detected in isolation because physical charge transfer occurs via complete electrons or protons, not portions of them.
7. What is Coulomb’s Law and why is it significant for board marking schemes?
Coulomb’s Law states that the electrostatic force between two point charges is directly proportional to the product of their charges and inversely proportional to the square of the distance between them: F = k × q1 × q2 / r2, where k is Coulomb's constant. This law forms the basis for many calculation-based and conceptual questions in board exams.
8. Give examples of how electric charge is generated by friction and its significance in real-life applications.
When two different materials are rubbed together (like glass and silk), electrons transfer from one to the other, causing one to become positively and the other negatively charged. Such principles explain phenomena like static electricity, lightning, and are applied in devices like photocopiers and electrostatic precipitators.
9. How does the law of conservation of charge apply to chemical and physical processes studied in the CBSE syllabus?
The law of conservation of charge states that the total electric charge remains constant in any isolated system during chemical or physical changes. For example, during electrolysis or even when rubbing objects, charges may move but their total never increases or decreases.
10. What experimental observation confirms the existence of two types of electric charges?
By rubbing glass rods with silk and bringing them near each other or near differently charged objects, observation of repulsion between like charges and attraction between unlike charges confirms the existence of both positive and negative electric charges.
11. Why is repulsion considered a decisive test for identifying the nature of electric charge during exams?
Repulsion occurs exclusively between like charges, while attraction can happen between unlike charges or charged and neutral objects. Therefore, observing repulsion assures that two objects carry charges of the same type, making it a sure test for charge identification.
12. How should students structure long-answer responses about electric charge to maximize marks, based on board exam patterns?
For high-mark responses, students should:
- Begin with a clear definition
- Explain key properties (additivity, quantization, conservation)
- Add examples or diagrams when possible
- Conclude with the relevance or application to real-world or syllabus topics
This method matches the CBSE marking scheme and helps gain full marks.
13. What happens when a neutral object is brought close to a charged object, and how is induced charge explained in CBSE Physics?
A charged object near a neutral one causes charges within the neutral object to redistribute (induction), resulting in the opposite type of charge being attracted closer, leading to an attractive force. This principle is fundamental in explaining many electrostatic phenomena discussed in NCERT textbooks.
14. In what way is electric charge both a scalar and a quantized property, and why is this important for calculation-based questions?
Electric charge is a scalar quantity because it has magnitude but no specific direction. It is also quantized, as charges only exist in integer multiples of e. These features simplify calculations in numericals, as charges are added algebraically and not vectorially.
15. How do charged particles behave in combined electric and magnetic fields, and why is this concept important for future competitive exams?
Charged particles experience force in both electric (F = qE) and magnetic fields (F = qvB sinθ). The resultant motion, described by the Lorentz force, forms the basis for many problems in advanced exams and core concepts in the CBSE Physics syllabus, linking theory to practical devices like cathode ray tubes and particle accelerators.
