A charge q1 exerts a force on another charge q2. If a third charge q3 is now brought close to them, the force exerted by q1 on q2 will:

Decrease
Increase
Remain unchanged
Increase if q3 has the same sign as q1, and decrease if it has the opposite sign

Correct answer: Remain unchanged

Solution

By Coulomb's law, the force on q2 due to q1 depends only on q1, q2 and the distance between them. A third charge q3 adds its own independent force on q2 (superposition), but it does not alter the force that q1 itself exerts on q2. So that particular force remains unchanged.

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