Two point charges +3µC and +8µC repel each other with a force of 40N. If a charge of -5µC is added to each of them, the force between them will become:
Correct answer: A. -10N
- A. -10N
- B. +20N
- C. +10N
- D. -20N
Explanation
The new charges are q'₁ = (+3 - 5)µC = -2µC and q'₂ = (+8 - 5)µC = +3µC. The force is proportional to the product of the charges. The ratio of the new force to the old force is F'/F = (q'₁q'₂)/(q₁q₂) = (-2)(+3)/(+3)(+8) = -6/24 = -1/4. So, F' = -F/4 = -40N/4 = -10N (attractive).
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