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−−6 µCr = 8 cm

Two point charges of −3 µC and −6 µC are 8 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −3 µCq2 = −6 µCr = 8 cm
F = N
2.Easy
−−3 µC−−1 µCr = 3 cm

Two point charges of −3 µC and −1 µC are 3 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −3 µCq2 = −1 µCr = 3 cm
F = N
3.Medium
−−10 µC++8 µCr = 50 cm

Two identical small metal spheres carry charges of −10 µC and +8 µC. They are touched together and then put back 50 cm apart. Find the magnitude of the force F between them now. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −10 µCq2 = +8 µCr = 50 cm
F = N
4.Medium
−−8 µC++4 µC−−2 µC20 cm + 20 cm

Three point charges lie on a straight line: −8 µC on the left, −2 µC on the right 40 cm away, and +4 µC between them, 20 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 = +4 µCrL = 20 cmrR = 20 cm
F = N
5.Hard
4 cm4 cm+q1​ = +2 µC+q3​ = +8 µC+q2​ = +2 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 8 µC is at the right-angle corner, q₁ = 2 µC is 4 cm from it along one side and q₂ = 2 µC is 4 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 2 µCq2 = 2 µCq3 = 8 µCr13 = 4 cmr23 = 4 cm
F = N
6.Hard
L = 40 cm5°qq

Two identical small balls, each of mass 1 g, hang from the same point on insulating threads 40 cm long. They are given equal charges and each thread settles at 5° 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 = 1 gL = 40 cmθ = 5°g = 9.81 m/s²
q = nC

Answer key

  1. 1. F = 25.28 N
  2. 2. F = 29.97 N
  3. 3. F = 0.03596 N
  4. 4. F = 5.394 N
  5. 5. F = 127.1 N
  6. 6. q = 21.54 nC

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