Physics Chapter 12.1: Coulomb's Law

Charges and Their Interaction

• Two types of electric charges exist: positive (protons) and negative (electrons).
• Like charges repel each other, while unlike charges attract each other.

Historical Context

• Charles Coulomb conducted the first measurement of electric force in 1874.
• His experiments led to the formulation of Coulomb's law.

Coulomb's Law

• Coulomb's law quantifies the force between two point charges.
• The force (F) is directly proportional to the product of the magnitudes of the charges (q1 and q2).
• The force is inversely proportional to the square of the distance (r) between the charges.
• Mathematically expressed as:
  • F ∝ (q1 * q2) / (r²)
  • F = k * (q1 * q2) / (r²)

Force Characteristics

• F is the magnitude of the mutual force acting on the charges.
• Force acts along the line that connects the two charges.
• 'k' represents the constant of proportionality.

Coulomb's Constant

• The value of 'k' varies with the medium between charges and the unit system used.
• For free space and SI units:
  • ( k = \frac{1}{4 \pi \epsilon_0} )
  • ( \epsilon_0 ) is the permittivity of free space, valued at ( 8.85 \times 10^{-12} , \text{Nm}^2/\text{C}^2 ).
• Substitute to find ( k = 9 \times 10^9 , \text{N m}^2/\text{C}^2 ).

Coulomb's Force in Free Space

• The expression for Coulomb's force in free space becomes:
  • ( F = \frac{1}{4 \pi \epsilon_0} \cdot \frac{q1 \cdot q2}{r^2} )