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++6 µCr = ?

Point charges of +6 µC and +6 µC exert a force of 10 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 = +6 µCF = 10 N
r = cm
2.Easy
−−80 nCPr = 40 cm

Find the magnitude of the electric field E at a distance of 40 cm from a point charge of −80 nC. Use k = 8.99 × 10⁹ N·m²/C².

q = −80 nCr = 40 cm
E = N/C
3.Medium
−−8 µC++10 µCr = 25 cm

Two identical small metal spheres carry charges of −8 µC and +10 µC. They are touched together and then put back 25 cm apart. Find the magnitude of the force F between them now. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −8 µCq2 = +10 µCr = 25 cm
F = N
4.Medium
++8 µC−−3 µCr = 25 cm

Two identical small metal spheres carry charges of +8 µC and −3 µC. They are touched together and then put back 25 cm apart. Find the magnitude of the force F between them now. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +8 µCq2 = −3 µCr = 25 cm
F = N
5.Hard
5 cm4 cm+q1​ = +1 µC+q3​ = +4 µC+q2​ = +10 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 4 µC is at the right-angle corner, q₁ = 1 µC is 5 cm from it along one side and q₂ = 10 µC is 4 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 1 µCq2 = 10 µCq3 = 4 µCr13 = 5 cmr23 = 4 cm
F = N
6.Hard
L = 80 cm10°qq

Two identical small balls, each of mass 8 g, hang from the same point on insulating threads 80 cm long. They are given equal charges and each thread settles at 10° 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 = 80 cmθ = 10°g = 9.81 m/s²
q = nC

Answer key

  1. 1. r = 17.99 cm
  2. 2. E = 4495 N/C
  3. 3. F = 0.1438 N
  4. 4. F = 0.899 N
  5. 5. F = 225.2 N
  6. 6. q = 344.7 nC

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