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Two point charges repel each other with force $F$. If the distance between them is doubled while both charges stay unchanged, the new force becomes
A$F/2$
B$F/4$
C$2F$
D$4F$
Answer & Solution
Correct answer: B. $F/4$
1. Coulomb's law: $F = k\frac{q_1 q_2}{r^2}$ — force is inverse-square in distance.
2. New distance $r' = 2r$, so $r'^2 = 4r^2$.
3. New force $F' = k\frac{q_1 q_2}{4r^2} = F/4$.
4. Option A treats the law as inverse-linear; options C and D have the force growing with distance, which contradicts the inverse-square law.
_Source: NCERT Class 12 Physics Ch 1 "Electric Charges and Fields", §1.6 Coulomb's Law_
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