Two point charges of 3 μC and 3 μC are 0.9 m apart in air. What is the force between them? (k = 9 × 10⁹ N m²/C²)
Answer and explanation
Correct answer: B. 0.1 N
- Step 1: Coulomb's law: F = kq₁q₂/r². Step 2. F = 9×10⁹ × (3×10⁻⁶) × (3×10⁻⁶) ÷ 0.9² = 0.1 N. Answer: 0.1 N. Why not the others: 0.09 N is what you get if you divide by r instead of r². 100 N is what you get if you make an error of 10³ in the microcoulombs. 0.01 N is what you get if you misplace a power of ten.
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