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 µCPr = 15 cm

Find the magnitude of the electric field E at a distance of 15 cm from a point charge of −5 µC. Use k = 8.99 × 10⁹ N·m²/C².

q = −5 µCr = 15 cm
E = N/C
2.Easy
++8 µC++3 µCr = ?

Point charges of +8 µC and +3 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 = +8 µCq2 = +3 µCF = 2 N
r = cm
3.Medium
++1 µC++4 µCP60 cm

A charge of +1 µC and a charge of +4 µC are 60 cm apart. Point P lies on the line between them, 36 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +1 µCq2 = +4 µCr1 = 36 cmr2 = 24 cm
E = N/C
4.Medium
−−10 µC−−5 µC++1 µC15 cm + 5 cm

Three point charges lie on a straight line: −10 µC on the left, +1 µC on the right 20 cm away, and −5 µC between them, 15 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 = −10 µCqR = +1 µCqM = −5 µCrL = 15 cmrR = 5 cm
F = N
5.Hard
4 cm6 cm+q1​ = +5 µC+q3​ = +2 µC+q2​ = +1 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 2 µC is at the right-angle corner, q₁ = 5 µC is 4 cm from it along one side and q₂ = 1 µC is 6 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 5 µCq2 = 1 µCq3 = 2 µCr13 = 4 cmr23 = 6 cm
F = N
6.Hard
L = 20 cm8°qq

Two identical small balls, each of mass 3 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 = 3 gL = 20 cmθ = 8°g = 9.81 m/s²
q = nC

Answer key

  1. 1. E = 1.998 × 10⁶ N/C
  2. 2. r = 32.85 cm
  3. 3. E = 554938 N/C
  4. 4. F = 37.96 N
  5. 5. F = 56.41 N
  6. 6. q = 37.76 nC

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