What is the magnitude of the electric field at 0.20 m from a point charge of 4.0 nC in air (k = 9.0 × 10⁹ N m² C⁻²)?
Correct answer D. 9.0 × 10² N/C
Explanation
E = kq/r² = 9.0 × 10⁹ × 4.0 × 10⁻⁹ / (0.20)² = 36/0.040 = 900 N/C. Dividing by r instead of r² gives 1.8 × 10² N/C.
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