Two charges repel with a force of 36 N. You triple the distance between them. Predict the new force, in newtons.

Estimate on a scale from 0 N (0) to 40 N (40).

Hints

Coulomb’s law is an inverse-square law: $F \propto 1/r^{2}$ .
Tripling $r$ divides the force by $3^{2} = 9$ .

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Why

$36/9 = 4$ N. Inverse-square dilution is geometric: the same "influence" spreads over a sphere whose area grows as $r^{2}$ , the same law gravity obeys.

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Two charges repel with a force of 36 N. You triple the distance between them. Predict the new force, in newtons.

Practise Electric Charge and Coulomb's Law

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