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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Electrostatics describes forces between charges through Coulomb's law, electric fields and field intensity, then uses electric potential to measure energy per unit charge. Capacitors store charge and electrical energy, with capacitance depending on geometry and dielectric material, not simply on the amount of charge present.
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