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
++4 µC++4 µCr = 25 cm

Two point charges of +4 µC and +4 µC are 25 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +4 µCq2 = +4 µCr = 25 cm
F = N
2.Easy
++3 µC++6 µCr = 6 cm

Two point charges of +3 µC and +6 µC are 6 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +3 µCq2 = +6 µCr = 6 cm
F = N
3.Medium
++8 µC−−4 µCP50 cm

A charge of +8 µC and a charge of −4 µC are 50 cm apart. Point P lies on the line between them, 25 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +8 µCq2 = −4 µCr1 = 25 cmr2 = 25 cm
E = N/C
4.Medium
−−5 µC++1 µCr = 5 cm

Two identical small metal spheres carry charges of −5 µC and +1 µC. They are touched together and then put back 5 cm apart. Find the magnitude of the force F between them now. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −5 µCq2 = +1 µCr = 5 cm
F = N
5.Hard
L = 100 cm20°qq

Two identical small balls, each of mass 5 g, hang from the same point on insulating threads 100 cm long. They are given equal charges and each thread settles at 20° 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 = 100 cmθ = 20°g = 9.81 m/s²
q = nC
6.Hard
L = 50 cm20°qq

Two identical small balls, each of mass 8 g, hang from the same point on insulating threads 50 cm long. They are given equal charges and each thread settles at 20° 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 = 50 cmθ = 20°g = 9.81 m/s²
q = nC

Answer key

  1. 1. F = 2.301 N
  2. 2. F = 44.95 N
  3. 3. E = 1.726 × 10⁶ N/C
  4. 4. F = 14.38 N
  5. 5. q = 963.9 nC
  6. 6. q = 609.7 nC

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