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Reviewed CSCA Physics question · Standard

A point charge Q = 2 x 10^-6 C produces an electric field. What is the magnitude of the electric field at a distance of 0.5 m from the charge? (Use k = 9 x 10^9 N m^2/C^2)

  1. 7.2 x 10^4 N/C
  2. 1.8 x 10^4 N/C
  3. 3.6 x 10^4 N/C
  4. 9 x 10^4 N/C
Show the answer and explanation

Correct answer

A. 7.2 x 10^4 N/C

Principle or equation

Electric field due to a point charge: E = k * |Q| / r^2.

Why this answer is correct

Substitute k = 9e9, Q = 2e-6, r = 0.5: E = (9e9 * 2e-6) / (0.5^2) = 18000 / 0.25 = 72000 N/C = 7.2 x 10^4 N/C.

Example

For Q = 1e-6 C at r = 1 m, E = 9e9 * 1e-6 / 1 = 9e3 N/C.

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