If two positively charged particles interact with a net charge of +1 and one particle is replaced by a +4 charge, at the same separation, how does the electrostatic force between them change?

If two positively charged particles interact with a net charge of +1 and one particle is replaced by a +4 charge, at the same separation, how does the electrostatic force between them change?

• A. It doubles
• B. It halves
• C. It becomes zero
• D. It quadruples

Answer: (D)

Coulomb’s law says the electrostatic force between two point charges is proportional to the product of the charges, with the separation fixed: F ∝ q1 q2 / r^2. If the second charge is kept the same and the first charge is replaced by a +4 charge, the product q1 q2 increases by a factor of 4. Therefore the force becomes four times larger. The net charge constraint doesn’t change this relation—the key is how the charges scale at fixed distance. Since both charges remain positive, the force is repulsive, and its magnitude increases fourfold.

Coulomb’s law says the electrostatic force between two point charges is proportional to the product of the charges, with the separation fixed: F ∝ q1 q2 / r^2. If the second charge is kept the same and the first charge is replaced by a +4 charge, the product q1 q2 increases by a factor of 4. Therefore the force becomes four times larger. The net charge constraint doesn’t change this relation—the key is how the charges scale at fixed distance. Since both charges remain positive, the force is repulsive, and its magnitude increases fourfold.