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 = ?

Point charges of +3 µC and +8 µC exert a force of 5 N on each other. How far apart r are they? Give the answer in cm. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +3 µCq2 = +8 µCF = 5 N
r = cm
2.Easy
−−1 µC−−3 µCr = 15 cm

Two point charges of −1 µC and −3 µC are 15 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −1 µCq2 = −3 µCr = 15 cm
F = N
3.Medium
−−10 µC−−10 µC++10 µC20 cm + 20 cm

Three point charges lie on a straight line: −10 µC on the left, +10 µC on the right 40 cm away, and −10 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 = −10 µCqR = +10 µCqM = −10 µCrL = 20 cmrR = 20 cm
F = N
4.Medium
++8 µC++2 µCP50 cm

A charge of +8 µC and a charge of +2 µC are 50 cm apart. Point P lies on the line between them, 37.5 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +8 µCq2 = +2 µCr1 = 37.5 cmr2 = 12.5 cm
E = N/C
5.Hard
L = 60 cm12°qq

Two identical small balls, each of mass 1 g, hang from the same point on insulating threads 60 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 = 1 gL = 60 cmθ = 12°g = 9.81 m/s²
q = nC
6.Hard
10 cm10 cm+q1​ = +4 µC+q3​ = +6 µC+q2​ = +6 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 6 µC is at the right-angle corner, q₁ = 4 µC is 10 cm from it along one side and q₂ = 6 µC is 10 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 4 µCq2 = 6 µCq3 = 6 µCr13 = 10 cmr23 = 10 cm
F = N

Answer key

  1. 1. r = 20.77 cm
  2. 2. F = 1.199 N
  3. 3. F = 44.95 N
  4. 4. E = 639289 N/C
  5. 5. q = 120.2 nC
  6. 6. F = 38.9 N

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