CLASS 12 PHYSICS REVISION NOTES
Chapter 1: Electric Charges and Fields
1. Electric Charge
Definition: The physical property of matter that causes it to experience a force when placed in an electromagnetic
field.
SI Unit: Coulomb (C)
Basic Properties:
• Quantization of Charge: Charge is always an integral multiple of the basic quantum of charge (e).
q=n·e
−19 C)
(where n is an integer and e = 1.6 × 10
• Conservation of Charge: The total charge of an isolated system remains constant over time.
• Additivity: The total charge of a system is the algebraic sum of all individual charges present anywhere on the
system.
2. Coulomb’s Law
States that the electrostatic force of interaction between two stationary point charges is directly proportional to the
product of their magnitudes and inversely proportional to the square of the distance between them.
F = 1/4πε · |q1q2|/r2
0
• ε is the permittivity of free space (≈ 8.854 × 10−12 C2/N·m2).
0
• The constant 1/ 9 2 2
4πε0 = 9 × 10 N·m /C .
3. Electric Field (E)
Definition: The electrostatic force experienced per unit positive test charge placed at that point without disturbing
the source charge.
E = F/q
0
Electric Field due to a Point Charge:
E = 1/4πε · q/r2
0
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Chapter 1: Electric Charges and Fields
1. Electric Charge
Definition: The physical property of matter that causes it to experience a force when placed in an electromagnetic
field.
SI Unit: Coulomb (C)
Basic Properties:
• Quantization of Charge: Charge is always an integral multiple of the basic quantum of charge (e).
q=n·e
−19 C)
(where n is an integer and e = 1.6 × 10
• Conservation of Charge: The total charge of an isolated system remains constant over time.
• Additivity: The total charge of a system is the algebraic sum of all individual charges present anywhere on the
system.
2. Coulomb’s Law
States that the electrostatic force of interaction between two stationary point charges is directly proportional to the
product of their magnitudes and inversely proportional to the square of the distance between them.
F = 1/4πε · |q1q2|/r2
0
• ε is the permittivity of free space (≈ 8.854 × 10−12 C2/N·m2).
0
• The constant 1/ 9 2 2
4πε0 = 9 × 10 N·m /C .
3. Electric Field (E)
Definition: The electrostatic force experienced per unit positive test charge placed at that point without disturbing
the source charge.
E = F/q
0
Electric Field due to a Point Charge:
E = 1/4πε · q/r2
0
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