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
−−5 µC++10 µCr = 10 cm

Two point charges of −5 µC and +10 µC are 10 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −5 µCq2 = +10 µCr = 10 cm
F = N
2.Easy
−−10 µC++5 µCr = 4 cm

Two point charges of −10 µC and +5 µC are 4 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −10 µCq2 = +5 µCr = 4 cm
F = N
3.Medium
++10 µC−−1 µCP10 cm

A charge of +10 µC and a charge of −1 µC are 10 cm apart. Point P lies on the line between them, 5 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +10 µCq2 = −1 µCr1 = 5 cmr2 = 5 cm
E = N/C
4.Medium
++5 µC++10 µC−−1 µC8 cm + 12 cm

Three point charges lie on a straight line: +5 µC on the left, −1 µC on the right 20 cm away, and +10 µC between them, 8 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 = +5 µCqR = −1 µCqM = +10 µCrL = 8 cmrR = 12 cm
F = N
5.Hard
L = 50 cm20°qq

Two identical small balls, each of mass 5 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 = 5 gL = 50 cmθ = 20°g = 9.81 m/s²
q = nC
6.Hard
10 cm3 cm+q1​ = +6 µC+q3​ = +2 µC+q2​ = +5 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 2 µC is at the right-angle corner, q₁ = 6 µC is 10 cm from it along one side and q₂ = 5 µC is 3 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 6 µCq2 = 5 µCq3 = 2 µCr13 = 10 cmr23 = 3 cm
F = N

Answer key

  1. 1. F = 44.95 N
  2. 2. F = 280.9 N
  3. 3. E = 3.956 × 10⁷ N/C
  4. 4. F = 76.48 N
  5. 5. q = 482 nC
  6. 6. F = 100.5 N

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