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
−−2 µC++5 µCr = 6 cm

Two point charges of −2 µC and +5 µC are 6 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −2 µCq2 = +5 µCr = 6 cm
F = N
2.Easy
++2 µC−−2 µCr = ?

Point charges of +2 µC and −2 µC exert a force of 20 N on each other. How far apart r are they? Give the answer in cm. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +2 µCq2 = −2 µCF = 20 N
r = cm
3.Medium
++1 µC−−1 µC−−4 µC16 cm + 24 cm

Three point charges lie on a straight line: +1 µC on the left, −4 µC on the right 40 cm away, and −1 µC between them, 16 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 = +1 µCqR = −4 µCqM = −1 µCrL = 16 cmrR = 24 cm
F = N
4.Medium
−−1 µC−−4 µCr = 25 cm

Two identical small metal spheres carry charges of −1 µC and −4 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 = −1 µCq2 = −4 µCr = 25 cm
F = N
5.Hard
L = 20 cm8°qq

Two identical small balls, each of mass 2 g, hang from the same point on insulating threads 20 cm long. They are given equal charges and each thread settles at 8° 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 = 2 gL = 20 cmθ = 8°g = 9.81 m/s²
q = nC
6.Hard
L = 40 cm15°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 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 = 1 gL = 40 cmθ = 15°g = 9.81 m/s²
q = nC

Answer key

  1. 1. F = 24.97 N
  2. 2. r = 4.24 cm
  3. 3. F = 0.9755 N
  4. 4. F = 0.899 N
  5. 5. q = 30.83 nC
  6. 6. q = 112 nC

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