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
++6 µC−−1 µCr = ?

Point charges of +6 µC and −1 µC exert a force of 8 N on each other. How far apart r are they? Give the answer in cm. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +6 µCq2 = −1 µCF = 8 N
r = cm
2.Easy
++1 µC−−8 µCr = 2 cm

Two point charges of +1 µC and −8 µC are 2 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +1 µCq2 = −8 µCr = 2 cm
F = N
3.Medium
++6 µC−−1 µCr = 30 cm

Two identical small metal spheres carry charges of +6 µC and −1 µC. They are touched together and then put back 30 cm apart. Find the magnitude of the force F between them now. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +6 µCq2 = −1 µCr = 30 cm
F = N
4.Medium
−−3 µC−−2 µC−−5 µC30 cm + 10 cm

Three point charges lie on a straight line: −3 µC on the left, −5 µC on the right 40 cm away, and −2 µC between them, 30 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 = −3 µCqR = −5 µCqM = −2 µCrL = 30 cmrR = 10 cm
F = N
5.Hard
L = 50 cm15°qq

Two identical small balls, each of mass 8 g, hang from the same point on insulating threads 50 cm long. They are given equal charges and each thread settles at 15° 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 = 50 cmθ = 15°g = 9.81 m/s²
q = nC
6.Hard
6 cm3 cm+q1​ = +1 µC+q3​ = +2 µC+q2​ = +8 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 2 µC is at the right-angle corner, q₁ = 1 µC is 6 cm from it along one side and q₂ = 8 µC is 3 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 1 µCq2 = 8 µCq3 = 2 µCr13 = 6 cmr23 = 3 cm
F = N

Answer key

  1. 1. r = 8.211 cm
  2. 2. F = 179.8 N
  3. 3. F = 0.6243 N
  4. 4. F = 8.391 N
  5. 5. q = 395.8 nC
  6. 6. F = 159.9 N

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