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++8 µCr = ?

Point charges of +6 µC and +8 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 = +6 µCq2 = +8 µCF = 2 N
r = cm
2.Easy
−−1 µC−−3 µCr = 10 cm

Two point charges of −1 µC and −3 µC are 10 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 = 10 cm
F = N
3.Medium
++6 µC−−5 µCP20 cm

A charge of +6 µC and a charge of −5 µC are 20 cm apart. Point P lies on the line between them, 8 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +6 µCq2 = −5 µCr1 = 8 cmr2 = 12 cm
E = N/C
4.Medium
++6 µC++2 µCP10 cm

A charge of +6 µC and a charge of +2 µC are 10 cm apart. Point P lies on the line between them, 6 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +6 µCq2 = +2 µCr1 = 6 cmr2 = 4 cm
E = N/C
5.Hard
L = 60 cm15°qq

Two identical small balls, each of mass 3 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 = 3 gL = 60 cmθ = 15°g = 9.81 m/s²
q = nC
6.Hard
L = 80 cm15°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 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 = 80 cmθ = 15°g = 9.81 m/s²
q = nC

Answer key

  1. 1. r = 46.45 cm
  2. 2. F = 2.697 N
  3. 3. E = 1.155 × 10⁷ N/C
  4. 4. E = 3.746 × 10⁶ N/C
  5. 5. q = 290.9 nC
  6. 6. q = 633.3 nC

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