Class 12 Physics – Chapter 1
Electric Charges & Fields
✍■ Handwritten■Style | Colourful | Board■Perfect Notes
■ Introduction
Electrostatics deals with electric charges at rest. This chapter is very important because it builds the base
for the entire electricity and magnetism unit. Most board questions are asked directly from the theory and
derivations of this chapter.
■ Electric Charge
Electric charge is a fundamental property of matter. It is responsible for all electrical effects that we
observe in nature.
• Two types of charges: Positive and Negative
• Like charges repel, unlike charges attract
• SI unit of charge is coulomb (C)
• Charge is quantized → q = ne
• Charge is conserved in an isolated system
Charge on electron: e = 1.6 × 10■¹■ C
■ Coulomb’s Law
According to Coulomb’s law, the electrostatic force between two stationary point charges is directly
proportional to the product of their charges and inversely proportional to the square of the distance
between them.
F = (πε■) × (q■q■ / r²)
The force acts along the line joining the two charges. It is repulsive for like charges and attractive for
unlike charges.
■ Electric Field
Electric field is introduced to explain action at a distance. It is defined as the force experienced by a unit
positive test charge.
E=F/q
■ Derivation: Electric Field due to a Point Charge
Consider a point charge q placed at the origin. A test charge q■ is placed at a distance r from it.
According to Coulomb’s law,
F = (πε■) × (q q■ / r²)
Electric field is force per unit charge. Therefore,
Electric Charges & Fields
✍■ Handwritten■Style | Colourful | Board■Perfect Notes
■ Introduction
Electrostatics deals with electric charges at rest. This chapter is very important because it builds the base
for the entire electricity and magnetism unit. Most board questions are asked directly from the theory and
derivations of this chapter.
■ Electric Charge
Electric charge is a fundamental property of matter. It is responsible for all electrical effects that we
observe in nature.
• Two types of charges: Positive and Negative
• Like charges repel, unlike charges attract
• SI unit of charge is coulomb (C)
• Charge is quantized → q = ne
• Charge is conserved in an isolated system
Charge on electron: e = 1.6 × 10■¹■ C
■ Coulomb’s Law
According to Coulomb’s law, the electrostatic force between two stationary point charges is directly
proportional to the product of their charges and inversely proportional to the square of the distance
between them.
F = (πε■) × (q■q■ / r²)
The force acts along the line joining the two charges. It is repulsive for like charges and attractive for
unlike charges.
■ Electric Field
Electric field is introduced to explain action at a distance. It is defined as the force experienced by a unit
positive test charge.
E=F/q
■ Derivation: Electric Field due to a Point Charge
Consider a point charge q placed at the origin. A test charge q■ is placed at a distance r from it.
According to Coulomb’s law,
F = (πε■) × (q q■ / r²)
Electric field is force per unit charge. Therefore,
