When two point charges are separated by a distance of 3 cm, the electric force between them is 300 n. what is the electric force between these two point charges when they are separated by a distance of 30 cm?

3 N

Explanation:

According to the Coulomb's law in electrostatics, the Coulomb force acting between two charges is directly proportional to the product of two charges and inversely proportional to the square of distance between them.

Case I :

F = 300 N, d = 33 cm

300 ∝ 1/ 3^2

300 ∝ 1/9     (1)

Case II:

Let F be the force, d = 30 cm

F ∝ 1/30^2

F ∝ 1/900     (2)

Dividing equation (2) by equation (1), we get

F / 300 = 9 / 900

F = 300 / 100

F = 3 N

current flows in a wire