Ans. COULOMB'S LAW
It states that,
The force of attraction Or repulsion between two point charges /s directly proportional to the product of the charges and inversely proportional to the square of the distance between them.
and Foc-j "
Combining Eq. (i) and (ii), we get
where F is the force between the two charges and is called the Coulomb's force, q, and q2 are the two charges and r is the distance between the centres of the two charges, k is the constant of proportionality and is equal to
The value of k depends upon the medium between the two charges and the system of units in which F, q and r are measured, e0 is the permitivity of free space.
Now if the medium between the two charges is air, then the value of k in SI units will be 9 x 109 Nm2C~2.