Coulomb's Law:Electric Force
🅸ntroduction
𝓣he physical quantity electric charge dominates in electrostatics as the nature has decorated it with a specific property - Charges can produce electric field within which they can interact mutually.They can exert the electrostatic force of attraction or of repulsion.What are the parameters of these forces? How can these be expressed mathematically? Very interesting, Coulomb has unveiled this mystery. Let us enjoy...
🆂tatement
𝓒oulomb's law states that the force of attraction or repulsion between two stationary 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.
If two point charges q₁ and q₂ are separated by distance r, then the force F of attraction or repulsion between them is given by
Where k is a constant of proportionality , called electrostatic force constant.The value of k depends on
❏ The nature of the medium between the two charges and
❏ The system of units chosen to measure F, q₁ , q₂ and r.
For the two charges located in free space and in SI units, we have
where ε₀ (epsilon naught) is called permittivity of free space.Value of ε₀ is
Here, 'F' is called Farad.
In vacuum
In a material medium
Where ε is permittivity of the medium and εᵣ is relative permittivity or dielectric constant of the given material medium .They are related as
🅲oulomb's law in vector form
𝓒onsider two positive point charges q₁ and q₂ placed in vacuum at distance r from each other . Being like charges , they repel each other.
In vector form , Coulomb's law may be expressed as