1. Quick Overview
Electric charge is one of the most fundamental concepts in
Electrical and Electronics Engineering. Every electrical and electronic device
operates because of the movement and interaction of electric charges.
Understanding electric charge is essential before studying electric current,
voltage, resistance, electrical circuits, and electronic devices.
Matter is made up of atoms, which contain positively charged
protons, negatively charged electrons, and neutral neutrons. The movement of
electrons from one atom to another creates electric current, making electric
charge the foundation of electricity.
The SI unit of electric charge is the Coulomb (C),
and its behavior is governed by the attraction and repulsion between charged
particles.
Learning Outcomes
After studying this topic, you will be able to:
- Define
electric charge.
- Identify
different types of electric charges.
- Understand
the properties of electric charge.
- Differentiate
between conductors and insulators.
- Explain
the importance of electric charge in electrical engineering.
2. Key Definitions
|
Term |
Definition |
|
Electric Charge |
A fundamental property of matter responsible for
electrical forces and electrical phenomena. |
|
Positive Charge |
Charge carried by protons. |
|
Negative Charge |
Charge carried by electrons. |
|
Neutral Body |
A body having equal numbers of protons and electrons. |
|
Electron |
A negatively charged subatomic particle that moves freely
in conductors. |
|
Proton |
A positively charged particle located inside the nucleus
of an atom. |
|
Neutron |
A neutral particle present in the nucleus of an atom. |
Important Facts
|
Property |
Value |
|
SI Unit |
Coulomb (C) |
|
Symbol |
Q |
|
Charge of Electron |
−1.602 × 10⁻¹⁹ C |
|
Charge of Proton |
+1.602 × 10⁻¹⁹ C |
|
Nature of Charge |
Scalar Quantity |
3. Working Principle / Concept
Electric charge is the basic property responsible for all
electrical effects.
Every atom contains:
- Positively
charged protons
- Negatively
charged electrons
- Neutral
neutrons
Normally, atoms contain equal numbers of protons and
electrons, making them electrically neutral.
When electrons move from one object to another, the object
gains or loses electric charge.
Types of Electric Charge
There are two types of electric charges:
- Positive
Charge (+)
- Negative
Charge (−)
Interaction Between Charges
- Like
charges repel each other.
- Unlike
charges attract each other.
Conservation of Charge
Electric charge can neither be created nor destroyed.
It can only be transferred from one body to another.
Quantization of Charge
Electric charge always exists in discrete quantities.
The smallest charge is the charge of one electron.
Comparison Table
|
Positive Charge |
Negative Charge |
|
Deficiency of electrons |
Excess of electrons |
|
Represented by (+) |
Represented by (−) |
|
Carried by protons |
Carried by electrons |
Conductors vs Insulators
|
Conductors |
Insulators |
|
Allow free movement of electrons |
Do not allow free movement of electrons |
|
Low resistance |
High resistance |
|
Copper, Aluminium |
Rubber, Glass, Plastic |
4. Important Formulae
Basic Formula
Electric Charge
Q = I × t
Where:
- Q =
Electric Charge (Coulomb)
- I =
Electric Current (Ampere)
- t =
Time (Second)
Formula Table
|
Formula |
Description |
SI Unit |
|
Q = I × t |
Electric Charge |
Coulomb (C) |
Important Electrical Quantities
|
Quantity |
Symbol |
SI Unit |
|
Electric Charge |
Q |
Coulomb (C) |
|
Current |
I |
Ampere (A) |
|
Time |
t |
Second (s) |
5. Diagram
Figure : Structure of an atom showing positively
charged protons, negatively charged electrons, and neutral neutrons.
6. Key Points for Exams
- Electric
charge is the fundamental property of matter responsible for electrical
phenomena.
- The
SI unit of electric charge is Coulomb (C).
- Electric
charge is represented by the symbol Q.
- There
are two types of electric charges: Positive and Negative.
- Like
charges repel each other, whereas unlike charges attract each other.
- Electric
charge follows the Law of Conservation of Charge.
- Electric
charge is quantized and exists in integral multiples of the electronic
charge.
- The
charge of one electron is −1.602 × 10⁻¹⁹ C.
- The
charge of one proton is +1.602 × 10⁻¹⁹ C.
- Movement
of electric charge produces electric current.
Quick Revision Table
|
Concept |
Key Point |
|
SI Unit |
Coulomb (C) |
|
Symbol |
Q |
|
Positive Charge |
Proton |
|
Negative Charge |
Electron |
|
Neutral Particle |
Neutron |
|
Current |
Flow of Electric Charge |
|
Like Charges |
Repel |
|
Unlike Charges |
Attract |
7. Advantages / Features
- Electric
charge is the basic building block of electricity.
- Helps
explain the operation of electrical and electronic devices.
- Forms
the basis for understanding current, voltage, and electric circuits.
- Essential
for studying electromagnetism and electrical engineering.
- Helps
in analysing electrical circuits and electronic components.
- Fundamental
concept for power systems and electronics.
Characteristics of Electric Charge
|
Characteristic |
Description |
|
Conserved |
Cannot be created or destroyed |
|
Quantized |
Exists in discrete quantities |
|
Scalar Quantity |
Has magnitude only |
|
Transferable |
Can move from one body to another |
|
Measurable |
Measured in Coulombs |
8. Limitations / Disadvantages
- Electric
charge itself cannot perform useful work unless it moves to form electric
current.
- Static
electric charges may cause unwanted electrostatic discharge (ESD).
- Excess
electric charge may damage sensitive electronic components.
- High
accumulation of charge can create sparks and electrical hazards.
- Charge
cannot exist independently without charged particles.
9. Applications
Electric charge plays an important role in almost every
electrical and electronic system.
Major Applications
|
Application |
Role of Electric Charge |
|
Batteries |
Store electric charge chemically |
|
Capacitors |
Store electric charge electrically |
|
Electric Circuits |
Flow of charge produces current |
|
Electric Vehicles |
Charge flows through motors and controllers |
|
Mobile Phones |
Operate using controlled movement of charge |
|
Computers |
Electronic charge represents digital information |
|
Electrostatic Painting |
Uses charged particles for uniform coating |
|
Photocopiers |
Uses electrostatic charge to transfer toner |
|
Lightning Protection |
Controls discharge of accumulated electric charge |
|
Semiconductor Devices |
Charge carriers enable device operation |
Real-Life Examples
- Charging
a mobile phone battery.
- Static
electricity generated by rubbing a balloon.
- Lightning
during thunderstorms.
- Capacitor
charging in electronic circuits.
- Flow
of current through household wiring.
10. Frequently Asked Viva Questions
Q1. What is electric charge?
Electric charge is a fundamental property of matter
responsible for electrical forces and electrical phenomena.
Q2. What is the SI unit of electric charge?
The SI unit of electric charge is the Coulomb (C).
Q3. What is the symbol of electric charge?
The symbol of electric charge is Q.
Q4. Name the two types of electric charge.
- Positive
Charge
- Negative
Charge
Q5. Which particle carries a negative charge?
The electron carries a negative charge.
Q6. Which particle carries a positive charge?
The proton carries a positive charge.
Q7. State the law of conservation of charge.
Electric charge can neither be created nor destroyed. It can
only be transferred from one body to another.
Q8. What is the formula for electric charge?
Q = I × t
where:
- Q
= Electric Charge
- I
= Electric Current
- t
= Time
Q9. What happens when like charges are brought together?
Like charges repel each other.
Q10. What happens when unlike charges are brought
together?
Unlike charges attract each other.