Coulomb’s law & electric fields worksheet with answers

Free printable Coulomb’s law & electric fields worksheet: 6 problems from easy to exam level, with an answer key. Print it or save it as a PDF.

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1.Easy
++8 µC++6 µCr = 12 cm

Two point charges of +8 µC and +6 µC are 12 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +8 µCq2 = +6 µCr = 12 cm
F = N
2.Easy
+q₁+q₂r

Two point charges repel each other with a force of 36 N. The first charge is doubled and the distance between the charges is halved. Find the new force F′.

F = 36 Nq₁′ = 2·q₁r′ = 0.5·r
F′ = N
3.Medium
++10 µC−−3 µCr = 25 cm

Two identical small metal spheres carry charges of +10 µC and −3 µC. They are touched together and then put back 25 cm apart. Find the magnitude of the force F between them now. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +10 µCq2 = −3 µCr = 25 cm
F = N
4.Medium
++10 µC−−3 µCr = 10 cm

Two identical small metal spheres carry charges of +10 µC and −3 µC. They are touched together and then put back 10 cm apart. Find the magnitude of the force F between them now. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +10 µCq2 = −3 µCr = 10 cm
F = N
5.Hard
+−P2 × 3 cm4 cm+2 µC−2 µC

Charges of +2 µC and −2 µC are 6 cm apart. Point P lies 4 cm from the midpoint between them, on the perpendicular bisector. Find the magnitude of the electric field E at P. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +2 µCq2 = −2 µCd = 6 cmh = 4 cm
E = N/C
6.Hard
L = 80 cm12°qq

Two identical small balls, each of mass 2 g, hang from the same point on insulating threads 80 cm long. They are given equal charges and each thread settles at 12° from the vertical. Use g = 9.81 m/s². Find the charge q on each ball in nC. Use k = 8.99 × 10⁹ N·m²/C².

m = 2 gL = 80 cmθ = 12°g = 9.81 m/s²
q = nC

Answer key

  1. 1. F = 29.97 N
  2. 2. F′ = 288 N
  3. 3. F = 1.762 N
  4. 4. F = 11.01 N
  5. 5. E = 8.63 × 10⁶ N/C
  6. 6. q = 226.6 nC

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