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
+q₁+q₂r

Two point charges repel each other with a force of 42 N. The first charge is tripled and the distance between the charges is made four times as large. Find the new force F′.

F = 42 Nq₁′ = 3·q₁r′ = 4·r
F′ = N
2.Easy
++3 µC−−10 µCr = 5 cm

Two point charges of +3 µC and −10 µC are 5 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +3 µCq2 = −10 µCr = 5 cm
F = N
3.Medium
++5 µC++5 µCP30 cm

A charge of +5 µC and a charge of +5 µC are 30 cm apart. Point P lies on the line between them, 12 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +5 µCq2 = +5 µCr1 = 12 cmr2 = 18 cm
E = N/C
4.Medium
++2 µC++1 µCP50 cm

A charge of +2 µC and a charge of +1 µC are 50 cm apart. Point P lies on the line between them, 12.5 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +2 µCq2 = +1 µCr1 = 12.5 cmr2 = 37.5 cm
E = N/C
5.Hard
L = 30 cm12°qq

Two identical small balls, each of mass 2 g, hang from the same point on insulating threads 30 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 = 30 cmθ = 12°g = 9.81 m/s²
q = nC
6.Hard
+−P2 × 4 cm8 cm+8 µC−8 µC

Charges of +8 µC and −8 µC are 8 cm apart. Point P lies 8 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 = +8 µCq2 = −8 µCd = 8 cmh = 8 cm
E = N/C

Answer key

  1. 1. F′ = 7.875 N
  2. 2. F = 107.9 N
  3. 3. E = 1.734 × 10⁶ N/C
  4. 4. E = 1.087 × 10⁶ N/C
  5. 5. q = 84.96 nC
  6. 6. E = 8.041 × 10⁶ N/C

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