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++5 µCr = ?

Point charges of +3 µC and +5 µC exert a force of 2 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 = +5 µCF = 2 N
r = cm
2.Easy
++3 µC++10 µCr = 25 cm

Two point charges of +3 µC and +10 µC are 25 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +3 µCq2 = +10 µCr = 25 cm
F = N
3.Medium
−−4 µC++5 µC−−1 µC6 cm + 4 cm

Three point charges lie on a straight line: −4 µC on the left, −1 µC on the right 10 cm away, and +5 µC between them, 6 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 = −4 µCqR = −1 µCqM = +5 µCrL = 6 cmrR = 4 cm
F = N
4.Medium
−−6 µC−−1 µCr = 40 cm

Two identical small metal spheres carry charges of −6 µC and −1 µC. They are touched together and then put back 40 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 = 40 cm
F = N
5.Hard
L = 60 cm15°qq

Two identical small balls, each of mass 5 g, hang from the same point on insulating threads 60 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 = 5 gL = 60 cmθ = 15°g = 9.81 m/s²
q = nC
6.Hard
+−P2 × 6 cm10 cm+4 µC−4 µC

Charges of +4 µC and −4 µC are 12 cm apart. Point P lies 10 cm from the midpoint between them, on the perpendicular bisector. Find the magnitude of the electric field E at P. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +4 µCq2 = −4 µCd = 12 cmh = 10 cm
E = N/C

Answer key

  1. 1. r = 25.97 cm
  2. 2. F = 4.315 N
  3. 3. F = 21.85 N
  4. 4. F = 0.6883 N
  5. 5. q = 375.5 nC
  6. 6. E = 2.721 × 10⁶ N/C

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