2. CONTENTS:
● Definition of Electric Charge
● Discovery of Electric Charge
● Types of Electric Charge
● What Type of Quantity Charge Is?
● Units of Charge
● Basic Properties of Electric Charge
● Coulomb's law of Electric Charge
● Methods of Charging An Neutral Body
3. Definition of Electric Charge:
Electric charge is a basic physical property associated with matter carried out by some
elementary particles like electrons, protons etc., due to which it produces and
experiences electric and magnetic effect.
It is because of these various objects exert strong electric forces of attraction or
repulsion on each other.
4. Discovery of Electric Charge:
Historically the credit of discovery of the fact that amber rubbed with wool or silk cloth
attracts light objects goes to Thales of Miletus, Greece around 600 BC.
In fact, the Greek name for amber is elektron which is
the origin of all such words: electricity, electric force,
electric charge and electron.
5. Types of Electric Charge:
Electric charges are of two general types:
• Positive Charge (+)
• Negative Charge (-)
A proton has a positive charge (+e) and an electron has a negative charge (-e).
If there is an excess of electrons, the body has a negative charge and an
excess of protons results in a positive charge.
6. What Type Quantity Charge Is?
Electric charge is a scaler quantity. It only has magnitude. There is no directions associated with a
electric charge so that it can be considered as a vector quantity.
Units of Electric Charge:
The SI unit of charge is Coulomb and the CGS unit of charge is esu (Electrostatic
Unit) or statcoulomb or franklin.
One Coulomb is written as 1 C.
1 C = 6.25 × 10¹⁸ or 6.24 quintillion electrons.
One Statcoulomb is written as 1 statC.
1 statC = 2.082 × 10⁹ electrons.
7. Basic Properties of Electric Charge:
It is observed from experiments that electric charges has following three basic properties:
•Additivity: Additivity of electric charge means that the total charge of a system is the
algebraic sum of all the individual charges located at different points inside the system.
If a system contains charges q1, q2, ........, qn, then its total charge is
q = q1 + q2 + .........+qn
•Quantization: The quantization of electric charge means that the total charge (q) of a body
is always an integral multiple of a basic quantum of charge (e), i.e.,
q = ne, where n = 0, ±1, ±2, ±3, ......... .
•Conservation: The law of conservation of electric charge which states :
→The total charge of an isolated system remains constant.
→ The electric charges can neither be created nor destroyed, they can only be transferred
from one body to another.
8. Coulomb's Law of Electric Charge:
In 1785, the French physicist Charles Augustin Coulomb experimentally measured the
electric forces between small charged spheres by using a torsion balance. He
formulated his observations in the form of Coulomb's law which is electrical analogue
of Newton's law of Universal Gravitation in mechanics.
This law states that the force of attraction or repulsion between two stationery point
charges is
• Directly proportional to the product of the magnitudes of the two charges and
• Inversely proportional to the square of the distance between them. This force acts
along the line joining the two charges.
9. Coulomb's Law of Electric Charge
If two point charges q1 and q2 are separated by distance r, then the force F for
attraction or repulsion between them is such that
F ∝ q1 q2 and F ∝ 1 / r²
∴ F ∝ q1 q2 / r² or F = K q1 q2 / r²
Where K is a constant of proportionality, called electro - static force constant.
