Kerala KEAM 5 June 2024 Solved Paper

The force between two charges $q_1$ and $q_2$ separated by a distance $r$ is given by Coulomb's law:$$F = k \frac{ | q_1 q_2 | }{r^2}$$where:- $k$ is Coulomb's constant,- $r$ is the distance between the charges.For the charges on spheres A and B, we are given:- $q_1 = 6 \, C$,- $q_2 = 12 \, C$,- The force between them is $F$.Now, we are asked to find the charge $q_1'$ that must be given to sphere A in order to reverse the direction of the force to $-F$. The charges should attract each other instead of repelling, meaning the product of the charges should become negative.To reverse the force direction, the charge $q_1'$ on sphere A must be:$$q_1' = -12 \, C$$Thus, the charge to be given to sphere A to reverse the force is $-12 \, C$.Therefore, the correct answer is:$$\boxed{-12 \, C}$$ Quick Tip: The force between two charges can be reversed by changing the sign of one of the charges. The magnitude of the force remains the same, but the direction is reversed.