Choose the correct statement regarding the validity of Coulomb's law.

1. Coulomb's law is valid for charges at rest.
2. Coulomb's law is valid for charges in motion.
3. Seperation between the charges must be greater then 10^-15 m.
4. It is valid only for point charges.

CONCEPT:   

Coulomb's law:

• Coulomb's law is a quantitative statement about the force between two-point charges at rest.
• When the linear size of charged bodies is much smaller than the distance separating them, the size may be ignored and the charged bodies are treated as point charges.
• Coulomb measured the force between two point charges and found that it varied inversely as the square of the distance between the charges and was directly proportional to the product of the magnitude of two charges and acted along the line joining the two charges.
• Mathematically it is written as,

\(\Rightarrow F = K\frac{q_1q_2}{r^2}\)

Where q1 = charge on 1st body, q2 = charge on a second body, and r = distance between two charged bodies.

EXPLAINATION:

Coulomb's law is valid when,

• From the above, it is clear that the charge is at rest
• The separation between charge must be greater than nuclear size(10^-15m) because for a distance less than (10-15m), strong nuclear forces dominate over electromotive force.
• From the above, the charges should be Point charge