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
−−3 µC−−8 µCr = 4 cm

Two point charges of −3 µC and −8 µC are 4 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −3 µCq2 = −8 µCr = 4 cm
F = N
2.Easy
−−3 µC++2 µCr = 4 cm

Two point charges of −3 µC and +2 µC are 4 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −3 µCq2 = +2 µCr = 4 cm
F = N
3.Medium
++8 µC−−8 µC−−2 µC5 cm + 5 cm

Three point charges lie on a straight line: +8 µC on the left, −2 µC on the right 10 cm away, and −8 µC between them, 5 cm from the left charge. Find the magnitude of the net electric force F on the middle charge. Use k = 8.99 × 10⁹ N·m²/C².

qL = +8 µCqR = −2 µCqM = −8 µCrL = 5 cmrR = 5 cm
F = N
4.Medium
++6 µC++8 µCP60 cm

A charge of +6 µC and a charge of +8 µC are 60 cm apart. Point P lies on the line between them, 30 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +6 µCq2 = +8 µCr1 = 30 cmr2 = 30 cm
E = N/C
5.Hard
4 cm3 cm+q1​ = +1 µC+q3​ = +3 µC+q2​ = +1 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 3 µC is at the right-angle corner, q₁ = 1 µC is 4 cm from it along one side and q₂ = 1 µC is 3 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 1 µCq2 = 1 µCq3 = 3 µCr13 = 4 cmr23 = 3 cm
F = N
6.Hard
L = 30 cm8°qq

Two identical small balls, each of mass 8 g, hang from the same point on insulating threads 30 cm long. They are given equal charges and each thread settles at 8° 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 = 8 gL = 30 cmθ = 8°g = 9.81 m/s²
q = nC

Answer key

  1. 1. F = 134.8 N
  2. 2. F = 33.71 N
  3. 3. F = 287.7 N
  4. 4. E = 199778 N/C
  5. 5. F = 34.38 N
  6. 6. q = 92.49 nC

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