Coulomb’s Law is a fundamental principle in physics that describes the electrostatic force between two charged objects. It is named after Charles-Augustin de Coulomb, who first published the law in 1785. Coulomb’s Law mathematically expresses the force between two point charges and is given by the equation:
[math]F=\frac{kq_1^2q_2^2}{r^2}[/math]
- F is the electrostatic force between the two charges,
- k is Coulomb’s constant, a proportionality constant that depends on the medium between the charges,
- q1 and q2 are the magnitudes of the two point charges,
- r is the separation distance between the charges.
Inverse Square Law:
The force is inversely proportional to the square of the separation distance between the charges. This means that if you double the distance between two charges, the force between them decreases by a factor of four , and if you triple the distance, the force decreases by a factor of nine, and so on.
Directly Proportional to Charges: The force is directly proportional to the product of the magnitudes of the two charges. If one or both charges increase, the force between them increases, and if one or both charges decrease, the force decreases.
Direction of Force:
Coulomb’s Law only provides the magnitude of the force. The direction of the force is along the line joining the two charges. The force is attractive if the charges are of opposite sign and repulsive if the charges have the same sign.
Coulomb’s Constant (k):
In a vacuum, Coulomb’s constant (k) is approximately 8.9875×10^9 N m^2/C^2. The value of k depends on the properties of the medium between the charges (such as permittivity).
The modified Coulomb’s Law in a material medium can be expressed as
[math]F = \frac{k_e \cdot |q_1 \cdot q_2|}{\epsilon_r \cdot r^2}[/math]
In this expression, the permittivity ε accounts for the influence of the medium on the electric field and force.